Catalytic application of dinuclear palladium(II) bis(thiosemicarbazone) complex in the Mizoroki-Heck reaction

Article abstract of DOI:10.1016/j.tetlet.2012.08.120

A convenient synthesis of new square planar dinuclear palladium(II) terephthaldehyde bis(thiosemicarbazone) complex has been described. The compositions of the complex have been established by elemental analysis, spectral methods and single crystal X-ray crystallographic technique. The new complex acts as an active recyclable homogeneous catalyst for the Mizoroki-Heck reaction of electron deficient (activating) and electron rich (deactivating) aryl halides with various olefins under optimized conditions.

Full text of DOI:10.1016/j.tetlet.2012.08.120

Tetrahedron Letters 53 (2012) 5961–5965
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Tetrahedron Letters
journal homepage: www.elsevier.com/locate/tetlet
Catalytic application of dinuclear palladium(II) bis(thiosemicarbazone)
complex in the Mizoroki-Heck reaction
⇑
Rupesh Narayana Prabhu, Rengan Ramesh
School of Chemistry, Bharathidasan University, Tiruchirappalli 620 024, Tamil Nadu, India
a r t i c l e i n f o
a b s t r a c t
Article history:
A convenient synthesis of new square planar dinuclear palladium(II) terephthaldehyde bis(thiosemicar-
bazone) complex has been described. The compositions of the complex have been established by elemen-
tal analysis, spectral methods and single crystal X-ray crystallographic technique. The new complex
acts as an active recyclable homogeneous catalyst for the Mizoroki-Heck reaction of electron deficient
Received 1 August 2012
Revised 27 August 2012
Accepted 28 August 2012
Available online 3 September 2012
(activating) and electron rich (deactivating) aryl halides with various olefins under optimized conditions.
Ó 2012 Elsevier Ltd. All rights reserved.
Keywords:
Bis(thiosemicarbazone) ligand
Dinuclear palladium(II) complex
Crystal structure
Mizoroki-Heck reaction
Carbon–carbon coupling reactions catalysed by transition metal
complexes are one of the most powerful and versatile tools in syn-
thetic organic chemistry.1 Mizoroki and Heck independently
reported the palladium(II)-mediated arylation of olefins using pal-
There have been a number of reports on the scope and versatility
of the Mizoroki-Heck reaction, giving emphasis to air and thermally
8
9
10
stable palladium catalysts, palladium nanoparticles, palladium
1
1
complexes containing sterically hindered phosphines, water solu-
2
12
13
ladium(II) salts. Several conditions have been developed since
ble catalysts and the use of molten salts as reaction media. Prom-
ising approaches for the coupling reaction of aryl bromides and
activated aryl chlorideshave been reported by using palladiumcom-
plexes as catalysts containing N-heterocyclic carbene ligands,
Schiff base ligands, pincer ligands, aniline ligands as well as
cyclometallated ligands containing phosphorous, nitrogen and
then for the palladium-catalysed Mizoroki-Heck cross-coupling
reaction of aryl halides with a wide range of olefinic substrates.
Unlike other C–C coupling reactions, the Mizoroki-Heck reaction
has the ability to tolerate a variety of functional groups (such as
unprotected amino, hydroxyl, aldehyde, ketone, carboxyl, ester,
cyano or nitro groups) thus avoiding the need for protection and
deprotection of functional groups during the organic transforma-
14
1
5
16
17
1
8
sulfur donor atoms. Immobilized and non-immobilized palladium
compounds have also been employed as effective catalysts for this
3
19
tions. Phosphorous-based ligands improve the catalytic activity
reaction.
of the Mizoroki-Heck reaction as a result of their increasing bulki-
ness and electron-donating functionality. The reactivity of the dif-
Thiosemicarbazones constitute an important class of Schiff base
ligands containing nitrogen and sulfur donor atoms for transition
metal ions exhibiting thione–thiol tautomerism in solution owing
to the presence of the –NH–C@S functional group. They are versa-
tile ligands exhibiting a wide range of coordination modes in their
metal complexes and bind to the metal ion in neutral or anionic
form, resulting in four- or five-membered chelate rings.20 A careful
view into the literature shows that there are several reports on the
4
ferent aryl halides decreases in the order ArI > ArBr > ArCl because
of the different strengths of the aryl-X bond (C–I < C–Br < C–Cl). For
the Mizoroki-Heck coupling reaction of aryl iodides with olefins,
5
very high turnover numbers (TON) have been reported already,
however, the search for efficient catalysts for the coupling of ole-
fins with deactivated aryl bromides and ultimately, towards acti-
6
21
vated aryl chlorides is under progress. A large number of reports
synthesis, characterization and biological applications of palla-
have been published on this coupling reaction ascertaining the
use of improved catalysts in order to obtain a higher TON and on
the influence of various factors such as reactants, catalysts and
additives on the rate of the reaction and the selectivity towards
dium(II) thiosemicarbazone complexes, however, there are only a
few reports on the use of Pd(II) thiosemicarbazone complexes as
catalysts for the Mizoroki-Heck reaction.
Though the Mizoroki-Heck reaction has been extensively stud-
ied using various palladium complexes, there is no report in the
literature where dinuclear palladium(II) bis(thiosemicarbazone)
complex was used as a catalyst for this reaction. We herein describe
the synthesis and characterization of new dinuclear palladium(II)
2
2
7
the desired products.
⇑
Corresponding author. Tel.: +91 431 240 7053; fax: +91 431 240 7045.
E-mail address: ramesh_bdu@yahoo.com (R. Ramesh).
0
040-4039/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.tetlet.2012.08.120

5
962
R. N. Prabhu, R. Ramesh / Tetrahedron Letters 53 (2012) 5961–5965
terephthaldehyde bis(thiosemicarbazone) complex incorporated
with bromide and triphenylphosphine as ancillary ligands.
The terephthaldehyde bis(thiosemicarbazone) ligand (L) was
prepared by the condensation of terephthaldehyde and thiosemi-
23
carbazide as reported in the literature. The ligand reacts with
PdBr (PPh ] in 1: 2 molar ratio in toluene and Et N for 6 h at
room temperature to give the new dinuclear Pd(II) complex of the
formula [Pd (L)Br (PPh ] (1) in 81% yield (Scheme 1). The oxida-
[
2
3
)
2
3
2
2
3 2
)
tion state of palladium remains unchanged during the formation
of the complex. The complex is air stable in both the solid and liquid
states at room temperature and is non-hygroscopic. The complex is
readily soluble only in highly polar solvents such as dimethyl form-
amide (DMF), dimethyl sulfoxide (DMSO) or N-methyl-2-pyrroli-
done (NMP) producing intense orange coloured solutions. The
elemental analysis data of the complex (Calcd: C, 47.00; H, 3.43;
N, 7.15; S, 5.46. Found: C, 47.09; H, 3.40; N, 7.19; S, 5.49) are in good
agreement with the molecular structure proposed.
Figure 1. ORTEP diagram of 1. DMSO with 30% probability. Selected bond lengths
(Å): Pd1–N1 2.106(5), Pd1–S1 2.2326(18), Pd1–P1 2.2594(16), Pd1–Br1 2.4534(9),
S1–C19 1.729(7), C19–N2 1.326(7), N1–N2 1.370(7), N1–C20 1.270(8). Selected
bond angles (°): N1–Pd1–S1 83.36(15), S1–Pd1–P1 92.12(6), P1–Pd1–Br1 88.56(5),
N1–Pd1–Br1 96.01(15), N1–Pd1–P1 175.10(15), S1–Pd1–Br1 178.35(5), C19–N2–
N1 113.4(5), C20–N1–N2 116.2(6), N2–C19–S1 125.8(6).
The FT-IR spectrum of the complex displays
mC@N stretch at
À1
1
589 cm which is at a lower frequency than that of the free
À1
ligand (1620 cm ) indicating coordination of azomethine nitrogen
to Pd(II) ion. The
C S
m @ and mN–H of the –N–NH–C@S group at
À1
À1
8
47 cm and 3203 cm , respectively in the free ligand disap-
peared in the complex suggesting enolization and subsequent
coordination through the thiolate sulfur to the Pd(II) ion.2 In the
electronic spectrum of the complex, the band below 350 nm is as-
signed to ligand centred transitions whereas the two strong bands
with absorption maxima at 390 nm and 411 nm and the weak
broad band at 490 nm are assigned to a combination of charge
4
3
one five-membered chelate ring. One PPh group (trans to the azo-
methine nitrogen) and one bromide ion (trans to thiolate sulfur)
also coordinate with the Pd(II) ion to form a BrNPS square plane.
The complex is having a distorted square planar geometry as re-
flected in all the bond parameters around Pd(II) ion. The crystal
structure also reveals the presence of one solvent molecule
(DMSO) of crystallization. The planar Pd units are slightly deviated
from planarity with the central phenylene moiety with a twist an-
gle of 7.30°. The bond lengths and bond angles are in good agree-
ment with the reported data on related Pd(II) thiosemicarbazone
25
transfer and d–d transitions.
In the 1H NMR spectrum of the complex, the aromatic protons
appeared as multiplets in the region of d 8.0–7.0 ppm. The singlet
due to azomethine proton (d 8.6 ppm) in the complex is slightly
downfield compared to the free ligand (d 8.0 ppm), suggesting
deshielding upon coordination to Pd(II) ion.26 The singlet that
appeared for the N–NH–C@S proton of the free ligand at d
29
complexes.
A careful view into the literature shows that the reaction condi-
tions such as solvent, base and reaction temperature have a dra-
matic influence on the yield of the Mizoroki-Heck reaction. In
order to optimize solvent, base and reaction temperature, the
Mizoroki-Heck cross-coupling reaction of 4-bromoacetophenone
with t-butyl acrylate using complex 1 as catalyst under various
reaction conditions was initially examined (Table 1). A controlled
experiment indicated that no cross-coupling product was observed
in the absence of the catalyst or base. The extent of conversion is
solvent-dependent and low conversions were observed in NMP
and DMSO as solvent even at higher temperature. DMF was found
to be the solvent of choice with excellent isolated yield even at a
lower temperature. A variety of inorganic and organic bases were
screened as the role of the base used is to neutralize and remove
HBr. The reaction rates were found to be strongly dependent on
the base employed. A remarkable increase in the product forma-
1
1.5 ppm is absent in the complex, supporting enolization and
13
coordination of the thiolate sulfur to the Pd(II) ion. The C NMR
of the complex shows resonances in the expected regions and the
complex revealed a downfield shift of the azomethine carbon rela-
tive to the free ligands indicating coordination of the azomethine
nitrogen to the metal centre. Also, the signal assigned to the thiok-
etone carbon, which moves upfield from d 178 ppm in the free li-
gand to d 170 ppm in the complex, results from the reduced C–S
bond order upon coordination.27 The P NMR spectra of the com-
plex showed a singlet resonance in the region of d 26.8 ppm in
31
2
8
agreement with the existence of equivalent phosphorus nuclei.
1
13
31
The H, C and P NMR spectra of the complex are given in Figure
S1–S3, Supplementary data.
Single crystal of the complex, 1, was obtained by the slow evap-
oration of DMSO solution of the complex at room temperature. The
molecular structure of the complex has been determined by single
crystal X-ray diffraction to confirm the coordination mode of
the ligand and geometry of the complex. The ORTEP view of com-
plex is shown in Figure 1. The ligand coordinates with each Pd(II)
ion via the azomethine nitrogen and the thiolate sulfur forming
tion was observed in the presence of inorganic bases like K
or Na CO . However, K CO being slightly more basic than Na
2
CO
CO
3
2
3
2
3
2
3
(entry 10) gave a higher conversion (entry 6). In the case of organic
bases such as triethylamine, pyridine or pyrrolidine, the yield of
the cross-coupled product was considerably reduced. The cross-
coupling reaction proceeds even at room temperature in DMF
using K
2
CO
3
as base, however, the reaction was slow with a lower
CO as
isolated yield even after 24 h. Thus it was concluded that K
2
3
H
2
N
H N
2
S
S
base in DMF solvent at 100 °C is the optimized condition for the
coupling reaction.
HN
N
[
PdBr
2
(PPh
3
)
2
]
PPh
3
Pd
Br
H
N
N
H
H
N
N
H
Br
Pd
It is preferred to use small amounts of catalyst and still achieve
high conversions in the Mizoroki-Heck cross-coupling reactions.
Also, it has been reported that low palladium catalyst loading is
required in some cases because the palladium black formation at
Toluene, Et
3
N
RT, 6 h
NH
NH
Ph
3
P
N
S
S
2
NH2
3
0
high catalyst loading inhibits the catalytic reaction. In order to
ascertain the efficiency of the catalyst, different catalyst: substrate
Scheme 1. Synthesis of dinuclear Pd(II) bis(thiosemicarbazone) complex.

R. N. Prabhu, R. Ramesh / Tetrahedron Letters 53 (2012) 5961–5965
5963
Table 1
100
a
Optimization of reaction conditions
O
Br
+
O
Complex 1
tBu
tBu
O
75
O
Solvent, base
O
O
5
0
5
0
Entry
Solvent
Base
Temp (°C)
Yieldb (%)
TONc
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
NMP
NMP
DMSO
DMSO
DMF
DMF
DMF
DMF
DMF
DMF
DMF
DMF
DMF
DMF
DMF
K
K
K
K
K
K
K
K
2
CO
2
CO
2
CO
2
CO
2
CO
2
CO
2
CO
2
CO
3
145
100
145
100
145
100
73
53
43
32
>99
>99
38
—
—
96
32
29
<15
<15
<15
730
530
430
320
990
990
380
—
3
3
3
3
3
3
3
2
d
25
0
4
8
12
Time (h)
16
20
24
e
100
100
100
100
100
100
100
100
—
—
0
1
2
3
4
5
Na
2
CO
3
960
320
290
<150
<150
<150
Figure 2. Influence of reaction time on isolated yield.
CH
CH
3
COOK
3
COONa
Et
3
N
Pyridine
Pyrrolidine
The progress of the formation of 4-acetyl-trans-cinnamic acid
tert-butyl ester from the cross-coupling reaction of 4-bromoaceto-
phenone and t-butyl acrylate as a function of time using complex 1
as catalyst is displayed in Figure 2. The reaction conditions were
similar to that given in Table 2, where 0.01 mol % of the complex
a
Reaction conditions: 4-bromoacetophenone (5 mmol), t-butyl acrylate
10 mmol), base (6 mmol), complex 1 (0.1 mol %), solvent (3 mL) for 8 h under N
atmosphere.
(
2
b
Isolated yield after column chromatography based on 4-bromoacetophenone
average of two runs).
1
is used. The results indicate that the formation of the cross-
(
c
coupled product increased initially with the progress of the
reaction time, reached a maximum and then remained unchanged.
Reasonably good isolated yield for the formation of the cross-
coupled product was observed at the optimum reaction time of
TON = Turnover number = ratio of moles of product formed to moles of catalyst
used.
d
Reaction carried out for 24 h.
Reaction carried out in the absence of catalyst.
e
8
h (94%) whereas over a period 15 h the maximum isolated yield
(
ꢀ96%) was achieved.
ratios were tested in the cross-coupling reaction of 4-bromoaceto-
phenone with t-butyl acrylate in the presence of complex 1 as cata-
lyst and the results are summarizedin Table 2. The reaction proceeds
with quantitative yield of the cross-coupled product when 1.0 or
Using the above optimized conditions, the Mizoroki-Heck cross-
coupling reaction of activated, non- and deactivated aryl bromides
with a variety of vinylic substrates (t-butyl acrylate, methyl acrylate,
styrene, 4-methyl styrene and 4-chloro styrene) was carried out
0
0
.1 mol % of the catalyst is used (entries 1 and 2). Even when
.01 mol % of the catalyst is used (entry 3), excellent isolated yield
2 3
with complex 1 as catalyst using DMF/K CO at 100 °C (Table 3).
Only trans products were obtained selectively in all the cases. In gen-
eral, for a particular aryl bromide, the cross-coupled products were
obtained in excellent isolated yield with t-butyl acrylate (entries 1–
of the cross-coupled product is obtained. Further, it was observed
that even under very low catalyst loading of 0.001 or 0.0001 mol %
(
entries 4 and 5), the reaction proceeds smoothly accompanied by
6
) or methyl acrylate (entries 7–12) as the vinylic substrate. The cor-
a drop in isolated yields. Interestingly these reactions can be con-
ducted with an ultra-low catalyst loading of 0.00001 mol % (entry
responding reactions with styrene as the olefinic partner gave
slightly lower yield (entries 13–18). Electron donating substituent
(
when compared to that of styrene, whereas electron withdrawing
substituent (4-chloro) on styrene gave slightly higher yield (entries
6
) with high turnover numbers (TON). Since the isolated yields are
4-methyl) on styrene gave slightly lower yield (entries 19–24)
good with appreciable TON when 0.01 mol % of catalyst is used, it
was concluded that this catalyst: substrate ratio is the best suitable
for the coupling reaction.
2
5–30) as that compared with styrene. It was also observed that for a
particular olefin, activated electron deficient aryl bromides (such as
-bromo-4-nitro benzene or 4-bromo acetophenone) could effec-
1
Table 2
Effect of catalyst loadinga
tively couple with the olefins providing the corresponding products
in excellent yield after 8 h. The non-activated electron neutral sub-
strate (bromo benzene) and deactivated electron rich substrates
(such as 4-bromo toluene, 4-bromo anisole and 4-bromo phenol)
gave moderate amount of products when coupling with the olefins.
All these indicated that the electronic effect of substituents on the
aryl bromides had great influence on the reaction and the electron
withdrawing substituents were more favourable for cross coupling.
The Mizoroki-Heck cross-coupling reaction of an activated aryl
chloride, 4-chloroacetophenone, with various olefinic substrates
O
Br
+
O
Complex 1
tBu
tBu
O
O
DMF, K
o
2 3
CO
1
00 C, 8 h
O
O
Yieldb (%)
TONc
Entry
Catalyst (mol %)
1
2
3
4
5
6
1.0
0.1
0.01
0.001
0.0001
0.00001
>99
>99
94
72
49
99
990
9400
72,000
490,000
11,00,000
2 3
was also investigated using complex 1 as the catalyst and K CO
as base in DMF at 100 °C (Table 4). It was observed that complex 1
acts as an active catalyst for the cross-coupling reaction of 4-chloro-
acetophenone with various olefins. However, compared to the bro-
mo analogue, the cross-coupling reaction of the chloro derivative is
sluggish even at higher catalyst loading and longer reaction time.
The recycling of the catalyst is one of the important aspects
for practical applications. The Mizoroki-Heck cross-coupling of
11
a
Reaction conditions: 4-bromoacetophenone (5 mmol), t-butyl acrylate
10 mmol), K CO (6 mmol), DMF (3 mL) at 100 °C for 8 h under N atmosphere.
Isolated yield after column chromatography based on 4-bromoacetophenone
(
(
2
3
2
b
average of two runs).
c
TON = Turnover number = ratio of moles of product formed to moles of catalyst
used.

5
964
R. N. Prabhu, R. Ramesh / Tetrahedron Letters 53 (2012) 5961–5965
Table 3
yield). After that, a gradual loss of activity was observed for the
Mizoroki-Heck reaction of aryl bromides with olefinsa
next three cycles with the isolated yields of ꢀ85%, ꢀ77% and
ꢀ65% for the fourth, fifth and sixth cycles. Though mononuclear
Pd(II) thiosemicarbazone complexes have been used as effective
Br
Complex 1
R1
R
1
+
DMF, K CO
2
3
2
2
R
0
R
1
00 C, 8 h
catalysts for the Mizoroki-Heck reaction, a direct comparison of
the mononuclear complexes with the dinuclear palladium(II)
bis(thiosemicarbazone) complex is difficult due to the difference
in the reaction conditions such as solvents, base, temperature,
reaction time and catalyst loading. The dinuclear Pd(II) bis(thio-
semicarbazone) complex can be synthesized conveniently from
inexpensive starting materials and obtained with satisfactory yield
making it a very promising catalyst. Further, a key advantage of the
ligand and complex over some others is that the reactions can
typically be performed in standard laboratory glassware without
dry-box technique.
Yieldb (%)
TONc
TOFd
Entry
–R
–R
1
t
1
2
3
4
5
6
7
8
9
–NO
–COCH
–H
2
–COO Bu
97
94
89
83
79
75
98
96
91
86
81
77
87
82
78
74
68
64
84
79
73
69
64
60
91
88
82
78
74
70
9700
9400
8900
8300
7900
7500
9800
9600
9100
8600
8100
7700
8700
8200
7800
7400
6800
6400
8400
7900
7300
6900
6400
6000
9100
8800
8200
7800
7400
7000
1213
1175
1113
1038
988
t
3
–COO Bu
t
–COO Bu
t
–CH
3
–COO Bu
t
–OCH
–OH
–NO
–COCH
–H
–CH
3
–OCH
–OH
–NO
–COCH
–H
3
–COO Bu
t
–COO Bu
938
2
–COOCH
–COOCH
–COOCH
–COOCH
–COOCH
–COOCH
3
1225
1200
1138
1075
1013
963
1088
1025
975
925
850
800
1050
988
913
863
800
750
1138
1100
1025
975
925
875
3
3
3
3
3
3
3
3
3
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
3
In conclusion, dinuclear Pd(II) complex bearing terephthalde-
hyde bis(thiosemicarbazone) ligand has been synthesized and
characterized. The single crystal X-ray evidenced the N and S coor-
dination mode of the ligand and a distorted square planar geome-
try around each Pd(II) ion. The new Pd(II) complex was found to be
highly efficient homogeneous catalyst for the Mizoroki-Heck reac-
tion of aryl bromides with various olefinic substrates with large
turnover numbers in relatively short times. The complex also acts
as an active catalyst for the Mizoroki-Heck cross-coupling reaction
of activated aryl chloride with various olefins.
2
–C
6
–C
6
–C
6
–C
6
–C
6
–C
6
–C
6
–C
6
–C
6
–C
6
–C
6
–C
6
–C
6
–C
6
–C
6
–C
6
–C
6
–C
6
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
5
5
5
5
5
5
4
4
4
4
4
4
4
4
4
4
4
4
–CH
3
–OCH
–OH
–NO
–COCH
–H
3
2
-4-CH
-4-CH
-4-CH
-4-CH
-4-CH
-4-CH
-4-Cl
-4-Cl
-4-Cl
-4-Cl
-4-Cl
-4-Cl
3
3
3
3
3
3
–CH
3
–OCH
–OH
–NO
–COCH
–H
3
Acknowledgments
2
We sincerely thank the Council of Scientific and Industrial
Research (CSIR), New Delhi, India, for financial support [09/
–CH
3
–OCH
–OH
3
4
75(0140)2008-EMR-I] and for Senior Research Fellowship to
R.N.P. We express sincere thanks to DST-FIST, India for the use of
Bruker 400 MHz spectrometer at the School of Chemistry, Bharath-
idasan University, Tiruchirappalli.
a
Reaction conditions: aryl bromide (5 mmol), olefin (10 mmol), K
complex 1 (0.01 mol %), DMF (3 mL) at 100 °C for 8 h under N
2
CO
3
(6 mmol),
2
atmosphere.
Isolated yield after column chromatography based on aryl bromide (average of
two runs).
b
c
TON = Turnover number = ratio of moles of product formed to moles of catalyst
used.
Supplementary data
d
TOF = Turnover frequency = TON per hour.
Supplementary data (Crystallographic data for the structural
analysis have been deposited with Cambridge crystallographic
center, CCDC No. 870247. Copies of this information may be ob-
tained free of charge from The Director, CCDC, 12 Union roads,
Cambridge CB2 1EZ, UK (email: deposit@ccdc.cam.ac.uk). The sum-
mary of the data collection and refinement parameters for the
4
-bromoacetophenone with t-butyl acrylate was selected to dem-
onstrate the feasibility of recycling usage with complex 1 as the
catalyst using DMF/K CO at 100 °C for 8 h in each run. The recy-
2
3
clability of the complex was investigated for six cycles. The catalyst
can be used three times without detectable loss of activity (isolated
1
13
31
complex; Experimental procedures; H, C and P NMR spectra
1
of the complex; H NMR data for all the Mizoroki-Heck coupling
products.) associated with this article can be found, in the online
version, at http://dx.doi.org/10.1016/j.tetlet.2012.08.120.
Table 4
Mizoroki-Heck reaction of 4-chloroacetophenone with olefinsa
References and notes
Cl
Co pl x 1
R1
R
1
+
DMF, K
0
2 3
CO
1.
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1
00 C, 24 h
O
Yieldb (%)
TONc
TOFd
2.
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Entry
–R
1
t
1
2
3
4
5
–COO Bu
–COOCH
44
46
35
30
38
440
460
350
300
380
18.3
19.2
14.6
12.5
15.6
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3
–C
6
–C
6
–C
6
H
H
H
5
4
4
-4-CH
-4-Cl
3
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a
Reaction conditions: 4-chloroacetophenone (5 mmol), olefin (10 mmol), K
6 mmol), complex (0.1 mol %), DMF (3 mL) at 100 °C for 24 h under
atmosphere.
Isolated yield after column chromatography based on 4-chloroacetophenone
average of two runs).
2
CO
N
3
2003, 22, 4715–4720.
(
1
2
6.
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b
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(
c
TON = Turnover number = ratio of moles of product formed to moles of catalyst
8.
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used.
d
TOF = Turnover frequency = TON per hour.

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1
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(