Synthesis and catalytic activities of 1-alkoxycarbonyl- and 1-carbamoylmethyl-5-phenyl-3-aryl-3H-imidazol-1-yliden-Pd(II) complexes

Article abstract of DOI:10.1016/j.jorganchem.2017.01.010

4-Phenyl-1-aryl-1H-imidazoles were reacted with α-haloesters and amides to give the corresponding imidazolium salts. The latter were used as starting materials for the synthesis of Pd(NHC) complexes. The catalytic activities of the newly prepared compounds were screened in a model coupling reaction. 1-Alkoxycarbonyl-5-phenyl-3-aryl-3H-imidazol-1-yliden-Pd(II) were shown to be better catalyst than the 1-carbamoylmethyl-5-phenyl-3-aryl-3H-imidazol-1-yliden-Pd(II) complexes. The catalysts were shown to be insensitive to the air oxygen and water.

Full text of DOI:10.1016/j.jorganchem.2017.01.010

Accepted Manuscript
Synthesis and catalytic activities of 1-alkoxycarbonyl- and 1-carbamoylmethyl-5-
phenyl-3-aryl-3H-imidazol-1-yliden-Pd(II) complexes
Meliha Çetin Korukçu, Necdet Coşkun
PII:
S0022-328X(17)30030-X
10.1016/j.jorganchem.2017.01.010
JOM 19767
DOI:
Reference:
To appear in: Journal of Organometallic Chemistry
Received Date: 9 August 2016
Revised Date: 16 January 2017
Accepted Date: 18 January 2017
Please cite this article as: M.E. Korukçu, N. Coşkun, Synthesis and catalytic activities of 1-
alkoxycarbonyl- and 1-carbamoylmethyl-5-phenyl-3-aryl-3H-imidazol-1-yliden-Pd(II) complexes, Journal
of Organometallic Chemistry (2017), doi: 10.1016/j.jorganchem.2017.01.010.
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ACCEPTED MANUSCRIPT
Synthesis and catalytic activities of 1-alkoxycarbonyl- and 1-
carbamoylmethyl-5-phenyl-3-aryl-3H-imidazol-1-yliden-Pd(II) complexes
Meliha Çetin Korukçu, Necdet Coşkun*
Uludağ University, Department of Chemistry, 16059-Bursa, TURKEY
coskun@uludag.edu.tr, 90224-2941725
Abstract: 4-Phenyl-1-aryl-1H-imidazoles were reacted with α-haloesters and amides to give the corresponding
imidazolium salts. The latter were used as starting materials for the synthesis of Pd(NHC) complexes. The
catalytic activities of the newly prepared compounds were screened in a model coupling reaction. 1-
Alkoxycarbonyl-5-phenyl-3-aryl-3H-imidazol-1-yliden-Pd(II) were shown to be better catalyst than the 1-
carbamoylmethyl-5-phenyl-3-aryl-3H-imidazol-1-yliden-Pd(II) complexes. The catalysts were shown to be
insensitive to the air oxygen and water.
Keywords: NHCs; NHC Enolates; Ag(I)-NHC complexes. Pd(II)-NHC complexes; Heck
reaction.
I. INTRODUCTION
The carbon-carbon bond forming reaction between alkenes and aryl halides in the presence of a
palladium catalyst has found an extensive usage following the pioneering reports of Mizoroki1 and
Heck2 from the early 1970s.
Numerous excellent surveys on a wide variety of different aspects of the Heck reaction have been
published.3 A variety of ligands3a have been developed for the reaction, and it has been a key step in the
total synthesis of many natural products and commercially important products.3b,3d The selectivity and
mechanistic aspects of the carbon-carbon bond forming reactions have been thoroughly reviewed,3c-e,4
and are still important subject of research.5 Our laboratory has recently described the utility of
isoxazolo[3,2-a]isoquinolines as precursors for the synthesis of stable azomethine ylides;6a while the
adducts of acyclic nitrones were shown to undergo a cascade reaction leading to the formation of
iminocarbenes.6b We have also reported the rearrangement of isoxazolines from the reaction of
imidazoline 3-oxides with dimethyl acetylenedicarboxylate to give the corresponding 3H-imidazol-1-
ium ylides. The reaction of the latter with AgNO3 in the presence of Et3N at room temperature provides
C-2 metallated N-heterocyclic carbine enolates (Ag-NHCE) precursors such as 1 (Scheme 1).7 The
silver compounds reported so far in the formation of Ag(I)-NHC complexes are AgOAc,8 Ag2O9 and
Ag2CO3.10 Silver N-heterocyclic carbene complexes have been important in the development of other
metal–carbene systems due to facile transmetallation reactions from the silver carbenes to a wide range
of other transition metals.11-12 Palladium complexes of NHC ligands, in particular, have proved to be
1

ACCEPTED MANUSCRIPT
excellent catalysts not only for the Heck reactions but also for the Suzuki, Stille and Sonagashira cross-
couplings.3e
Ph
Ph
CO2Me
CO2Me
Ph
ArN
O
N
Pd O
NAr
CO2Me
CO2Me
CO2Me
CO2Me
MeO2C
MeO2C
ArN
N
ArN
N
X Pd O
NEt3
Ag
N
O
NEt3
Ph
NHCE precursors 1
3
2
Figure 1. The structures of NHC Enolate precursors and Pd(II)-NHCE complexes
Recently we have demonstrated the utility of compounds 1 as N-heterocyclic carbene-enolate (NHCE)
ligand precursors.13 The reaction of 1 with equimolar Pd(II) salts in CH2Cl2 provides complexes 2 in
equilibrium with 3. The screen in coupling reactions (e.g. Heck and Suzuki) revealed their efficiencies
as catalysts at 80°C for the favorable combinations of aryl halide (electron deficient) and styrene
(electron rich) and 100 or 120 °C for the unfavorable cases (electron rich aryl halide and electron
deficient styrene). The catalysts were extremely effective in Suzuki reaction at room temperature and in
aqueous media. Hammett type correlations confirmed the effect of substituents on the aryl halide and
styrene to be opposite. The electron donating groups on the aryl halide decelerate while the same on the
styrene ring accelerate the coupling reaction rate. Similar effects were found for the Suzuki coupling
reaction: Electron-deficient aryl halides and electron-rich arylboronic acids are more reactive than the
corresponding electron rich aryl halide and electron-deficient boronic acids. Reasonable mechanisms for
these couplings in the presence of Pd-NHCE complexes were discussed. The synthetic potential of the
newly prepared catalysts were demonstrated in the synthesis of stylbenes, biaryls as well as arylated
heterocycles.
Ph
Ph
Ph
ArN
O
N
Pd O
NAr
R
ArN
N
ArN
N
R
R
X Pd O
NEt3
Ag
N
R
O
NEt3
Ph
NHCE precursors 1'
3'
2'
Figure 2. Structures of the expected NHC Enolate precursors and Pd(II)-NHCE complexes from 1-
alkoxycarbonyl- and carbamoylmethyl-5-phenyl-3-p-tolyl-3H-imidazol-1-ium salts.
2

ACCEPTED MANUSCRIPT
Encouraged by the above mentioned results we have planned to prepare a series of imidazole based salts
1’ and convert them to 2’ and 3’ and test their activity in a coupling reaction (e.g. Heck reaction). Here
we report on the unusual behaviour of imidazolium salts 5 in regard to their reactions with Ag2O and
AgNO3.
II. RESULTS AND DISCUSSION
II.1 Alkylations of imidazoles 4 with α-halocarbonyl compounds
The treatment of imidazoles 4 available by the previously reported methods7 with an excess of α-
halogenated ester in toluene at 90 oC provided compounds 5 in high yield and purity.14 The reaction of 4
with α-chloroamides at the same conditions was a very slow process, however the use of KI as a catalyst
provided the formation of 5 in high yields (Scheme 1 and Table 1). The elemental analyses and spectral
data confirmed the proposed structures.
i
R
N
R
N
X
N
N
O
R1
5
4
Scheme 1. Alkylations of imidazoles 4 with α-halocarbonyl compounds.
Reaction conditions: i) R1COCH2X, toluene, 90 oC, 18-24 h.
Table 1. Synthesis of 5 from the alkylations of 4 with α-halocarbonyl compounds
5
a
b
c
R
X
R1
Yieldb (%)
Mp (oC)
152–154
195–196
171–172
263–264
252–253
p-Me
p-MeO
p-Me
p-Me
p-Me
Br
Br
Br
Cl
Cl
OEt
76
87
84
75
73
OEt
O-(-)-menthyl
NH2
NHAra
d
e
aAr = 2,6-dimethylphenyl; bIsolated yield
II.2 Synthesis of Ag(I)- and Pd(II)-NHC complexes.
The treatment of compounds 5 in CH2Cl2 at room temperature with Ag2O in the presence of molecular
sieve15 provides complexes 6a-e in quantitative yields and high purity. The use of the protocol we
have recently reported7, 13 (Scheme 2, Table 2) ensures the formation of compounds 7a-e. The most
characteristic evidence for the formation of complexes 6 is the disappearance of the peak at ca 10 ppm
in the 1H NMR spectra of 5 due to metallation of C-2 carbon. The down-field shifts of C4-H peaks (ca
3

ACCEPTED MANUSCRIPT
0.5 ppm) in the imidazolium ring as well as the methylene protons (ca 0.2 ppm) points to an enhanced
electron density at the corresponding carbon atoms to which they are bounded. The Ag bounded
carbon resonates at ca 182.0 ppm in DMSO-d6.
Ph
Ph
i or ii
iii
R
N
R
N
N
N
5
-H
-AgX
Cl
XAg
Pd
R1
O
O
R1
Cl
8
6 (X=Br or Cl)
7 (X=NO3)
Scheme 2. Synthesis of Ag(I)- and Pd(II)-NHC complexes. Reaction conditions: i) Ag2O, molecular
sieve, CH2Cl2, rt 0.5 h ii) Et3N, AgNO3, CH2Cl2, rt, 1 h iii) Pd(CH3CN)2Cl2, CH2Cl2, rt 1 h.
Table 2. Synthesis of NHC-metal complexes 6-8.
Isolated Yield (%)
6-8
R
X for 6
X for 7
R1
6
7
8
8
Meth. Ab Meth. Bc
p
p
p
p
p
-Me
Br
Br
Br
Cl
Cl
NO3
NO3
NO3
NO3
NO3
OEt
OEt
98
96
81
85
77
75
83
93
95
92
76
93
89
86
92
91
72
a
b
c
-MeO
-Me
O
-(-)-menthyl 62
-Me
NH2
NHAra
40
67
d
e
-Me
aAr = 2,6-dimethylphenyl. bStarting from 6; cStarting from 7.
The treatment of compounds 6 or 7a-e with Pd(CH3CN)2Cl2 in dichloromethane16 at room temperature
for short time provides compounds 8 in high yields ( Scheme 2 and Table 2). The reactions were
1
monitored by H NMR. At the end of the reaction the characteristic peak of 6 and 7 at ca 5 ppm
assigned to the methylene protons disappears and the same peak for the product appears as an AB
system. The latter fact implies that the ester carbonyl is coordinated to the metal centre in such a way
that the symmetry of the molecule should be distorted. The carbene carbon in the 13C NMR spectra of
8 appears at 145.4 ppm. The HMBC spectra revealed also the presence of cross peaks with C-4H of the
imidazole ring.
II.3 Thermal reactions of complexes 7 and 8.
The thermal behaviours of complexes 7a-e were investigated under nitrogen atmosphere in the 25-950
oC range. Ester type complex 7a-b lose ethylene at around 120 oC (Scheme 3). In the case of cyclohexyl
ester 7c the low molecular compound lost is not the corresponding cyclohexene derivative but HBr,
4

ACCEPTED MANUSCRIPT
probably due to steric reasons the (-)-menthyl group can not provide a hydrogen coplanar with the
carbonyl group to undergo the expected fragmentation. The amide type complex 7d was shown to
undergo β-elimination at quite mild conditions, to give probably the corresponding ketene substituted
complex and NH3 (Scheme 4). The all above discussed thermal reactions in fact can find synthetic
applications in the design of new metallacyclic compounds.
Ph
Ph
Ph
-
N
R
R
N
R
N
N
N
N
Ag
(O3N)Ag
(O3N)Ag
HO
O
O
O
H
7a'-b''
7a'-b'
7a-b
Ph
Ph
- HNO3
N
N
N
N
H
O
Ag
O
(O3N)Ag
O
O
7c'
7c
Scheme 3. Thermal decomposition pathways for 1-alkoxycarbonyl-5-phenyl-3-p-tolyl-3H-imidazol-1-
yliden-Ag(I) complexes 7a-c.
H
Ph
-NH3
Ph
N
R
N
N
N
H
(O3N)Ag
(O3N)Ag
O
NH2
O
7d''
7d
Ph
Ph
N
N
N
N
O3NAg
Ag
O
NH
7e'
7e
Scheme 4. Decomposition pattern of 1-carbamoylmethyl-5-phenyl-3-p-tolyl-3H-imidazol-1- yliden-
Ag(I) complexes 7d-e.
5

ACCEPTED MANUSCRIPT
Pd-NHC complex 8a-b behaves as their silver analogues 7a-b. The loss of ethylene occurs even at a
o
little lower temperature, 113 C (Scheme 5). TGA analysis revealed that the compound forming 8a’-b’
o
after the loss of ethylene is stable to 225 C. This should be taken in consideration for the catalytic
species in the reactions performed over 113 oC. The heating of 8c produces 8c’, a decomposition pattern
similar to those of silver complex 7c. Amide type Pd-complexes 8d-e behaves differently from the
corresponding silver complexes (Scheme 6). The heating of the latter under nitrogen lead to the
elimination of HCl probably due to intramolecular substitution at the metal centre to produce the
corresponding cyclic structures 8d’-e’ as depicted in Scheme 6.
Ph
Ph
-
R
N
N
R
N
N
Cl Pd
Cl
O
Cl Pd
Cl
O
O
O
8a'-b'
H
H
8a-b
Ph
H
N
N
Ph
Cl Pd
O
H
O
N
N
O
O
H
Pd Cl
Cl Pd
O
O
N
N
Cl
8c
8c'
Ph
Scheme 5. Thermal decomposition pathways for 1-alkoxycarbonyl-5-phenyl-3-p-tolyl-3H-imidazol-1-
yliden-Pd(II) complexes 8a-c.
6

ACCEPTED MANUSCRIPT
Ph
Ph
N
N
-HCl
Cl Pd
NH
N
N
O
O
HN
8d'
H
Pd Cl
Cl Pd
Cl
N
H
O
N
N
8d
Ph
Ph
Ph
N
N
-HCl
N
N
Cl Pd
N
O
Cl Pd
Cl
N
H
O
O
N
Pd Cl
N
N
8e
8e'
Ph
Scheme 6. Decomposition pattern of 1-carbamoylmethyl-5-phenyl-3-p-tolyl-3H-imidazol-1- yliden-
Pd(II) complexes 8d-e.
II.4 Optimization of the Heck reaction conditions for the styrene arylation in the presence
of NHC-Pd complex 6.
To determine the best catalyst in the series 8a-e the arylation of styrene (Scheme 7) was performed in
DMF in the presence of NaAcO as a base, Table 3 entries 1-5. The total conversions were followed by
1H NMR and the kinetic curves depicted in Figure 3.
100
80
60
40
20
0
100
80
60
40
20
0
Cs2CO3
Na2CO3
K2CO3
NaHCO3
NaOAc
8a
8b
8c
8d
8e
0
10
20
30
40
50
60
70
0
10
20
30
40
50
Time (h)
Time (h)
Figure 3. Catalitic efficiencies of 8a-e (left graph) and effect of the base on the catalytic activity with 8a in DMF
at 120 oC.
7

ACCEPTED MANUSCRIPT
Albeit a comparison of the initial conversion rates shows that 8a is superior to all other at the end of
the reactions 8b successfully competes with it. As a whole, ester type complexes are better catalyst
than the amide type 8d-e. Therefore, we have selected 8a as a lead and searched for the best base in
DMF, Table 3, entries 6-9. The reactions were performed with 1 mol% catalyst and as is shown in
Figure 3, the right graph, Cs2CO3, NaOAc and Na2CO3 provide nearly the same conversion rates. Due
to the higher selectivity in the case of NaOAc we have selected it for the experiments to reveal the
solvent effect, Table 3, entries 1,10-12, Figure 4, left graph.
95
100
90
80
85
80
60
75
40
DMAA
70
NMP
DMF-H2O
DMF
20
65
60
0
10
20
30
40
50
0
10
20
30
40
50
H2O conc (%)
Time (h)
Figure 4. Solvent (left) and water concentration in DMF effect.
Reaction
O
conditions
+
Y
Table 3
O
9
10
11
Scheme 7. Arylation of styrene with 4-bromobenzaldehyde in the presence of compounds 8.
Surprisingly DMF-H2O mixture (1:1) was as equally good as all other solvents. To prove the effect of
water concentration on the conversion rate of the model Heck reaction we have used different
concentrations (Table 3, entries 13-17). The results are plotted in Figure 4, the right graph. There was
not a linear increase or decrease, instead a polynomial changes at the 99th hours of the reaction were
determined. After optimization of the solvent and the base the model reaction was performed in the
presence of 8a with 0.1, 0.01, 0.001 and 0.0001 mol% concentrations (Table 3, entries 18-21). The
experiments revealed that TON’s of 104 can be achieved with high regio- and diastereoselectivity.
Table 3. Substituent, solvent and base effect in the Heck-Mizoroki reaction catalyzed by compounds 8.
Entry Cat
Y
Cat.
mol %
1
Base
Base Solvent
eqv
Time Total
(h)
TONmax
aconvrsn
Br
Br
NaOAc
NaOAc
4
DMF
67
100
100
100
1
2
8a
8b
1
4
DMF
67
100
8

ACCEPTED4MANUSCRIPT
Br
Br
Br
Br
Br
Br
Br
Br
Br
Br
1
1
1
1
1
1
1
1
1
1
NaOAc
NaOAc
NaOAc
Cs2CO3
Na2CO3
K2CO3
DMF
DMF
DMF
DMF
DMF
DMF
DMF
DMAA
NMP
67
67
67
43
43
43
43
43
43
43
87
87
3
8c
8d
8e
8a
8a
8a
8a
8a
8a
8a
4
4
2
2
2
4
4
4
4
81
81
4
75
75
5
96b
96
6
77
77
7
13c
96
13
8
NaHCO3
NaOAc
NaOAc
NaOAc
96
9
100
100
100
100
100
100
10
11
12
DMF-H2O
(5:5)
Br
Br
Br
Br
Br
0.1
0.1
0.1
0.1
0.1
NaOAc
NaOAc
NaOAc
NaOAc
NaOAc
4
4
4
4
4
DMF-H2O
(9:1)
DMF-H2O
(8:2)
DMF-H2O
(7:3)
DMF-H2O
(6:4)
99
99
99
99
99
72
68
86
80
91
720
680
860
800
910
13
14
15
16
17
8a
8a
8a
8a
8a
DMF-H2O
(5:5)
Br
Br
Br
Br
Cl
0.1
NaOAc
NaOAc
NaOAc
4
4
4
4
4
DMF
99
99
99
99
21
63
33
0
630
18
19
20
21
22
8a
8a
8a
8a
8a
0.01
0.001
DMF
DMF
DMF
DMF
3300
0.0001 NaOAc
NaOAc
0
1
0
aNo Pd black formations was observed. bThe Z-isomer is forming in 20% yield. cBenzaldehyde is forming in 3%.
Catalyst 8a was also screened for its activity in the reaction of 4-chlorobenzaldehyde with styrene,
however no conversion was observed, Entry 22.
III. CONCLUSIONS
Thus, imidazolium salts 5 react with Ag2O and AgNO3 in the presence of Et3N to give Ag-NHC and Pd-
NHC complexes instead of the expected NHC Enolate precursors. The transmetallation reaction of the
latter give again the Pd(II)NHC complexes contrary to our expectations (Figure 2). The thermal analysis
of the latter complexes revealed interesting synthetically useful transformations depending on the
structure of the aliphatic substituent on the N-1 of the NHC ligand. Structure and catalytic activity
screen for compounds 8 have shown that 1-alkoxycarbonyl-5-phenyl-3-aryl-3H-imidazol-1-yliden-
Pd(II) are better catalyst than the 1-carbamoylmethyl-5-phenyl-3-aryl-3H-imidazol-1-yliden-Pd(II)
9

ACCEPTED MANUSCRIPT
complexes. Having in mind the thermal transformations shown by TGA we can conclude that at the
temperature we have conducted the model reaction the precatalyst is the corresponding 8’. The
preparation, characterisation and screening their catalytic potential in some other coupling reactions is
underway.
IV. EXPERIMENTAL
IV.1 General
Melting points were recorded on an Electrothermal Digital melting point apparatus. Infrared spectra
were recorded on a Thermo-Nicolet 6700 FTIR. 1D and 2D NMR experiments were performed on a
Varian Mercury Plus 400 MHz spectrometer. The elemental analyses were performed on a EuroEA
3000 CHNS analyser. Thermogravimetric curves were obtained using a SII Exstar TG/DTA 6200
analyzer in the range 25-1000 oC in platinum crucibles under nitrogen at a heating rate of 10 oC min-1
using alumina as reference.
IV.2 Synthesis of 1-alkoxycarbonyl-5-phenyl-3-p-tolyl-3H-imidazol-1-ium salts (5a-c). General
Procedure: To a solution of imidazole 4 (1 mmol) in toluene (3 mL) alkyl bromoacetate (3 mmol) was
added and the reaction mixture stirred for 18 h at 90 oC. The precipitated product was filtered, washed
with toluene (3X5 mL) and dried under vacuum.
IV.3 Synthesis of 1-carbamoylmethyl-5-phenyl-3-p-tolyl-3H-imidazol-1-ium salts (5d-e). General
Procedure: To a solution of imidazole 4 (1 mmol) in toluene (3 mL) α-haloamide (3 mmol and KI
(0.3 mmol, 0.050 g) were added and the reaction mixture stirred for 24 hrs at 90 oC. In the case of 4d
the solvent was evaporated and the crude mixture washed with toluene (3X5 mL) and CH2Cl2 (6X5
mL). In the case of 4e the solvent was evaporated and the solid mixture was washed with hot toluene
(5X5 mL).The residual solids were dried under vacuum.
1-Ethoxycarbonylmethyl-5-phenyl-3-(p-tolyl)-3H-imidazol-1-ium bromide 5a. Yield 0.305 g,
76%. Colourless crystals, mp 152–154 oC. IR (KBr) νC=O 1744 cm-1; 1H NMR (400 MHz, DMSO-d6):
δ 1.06 (3H, t, J = 6.8 Hz), 2.40 (3H, s), 4.07 (2H, q, J = 6.8 Hz), 5.33
Ph
(2H, s), 7.49 (2H, d, J = 8.0 Hz), 7.58 (5H, s), 7.74 (2H, d, J = 8.0 Hz),
N
Br
N
13
8.58 (1H, d, J = 1.2 Hz), 9.99 (1H, d, J = 1.2 Hz). C NMR (100
O
O
MHz, DMSO-d6): δ 14.2; 21.1; 48.9; 62.6; 119.7; 121.9; 125.2; 129.6;
129.8; 131.0; 131.2; 132.6; 135.7; 137.3; 140.5; 166.6. Anal. Calcd
for C20H21BrN2O2 (401.30 ) C, 59.86; H, 5.27; N, 6.98; Found C,
60.00; H, 4.95; N, 7.30.
5a
10

ACCEPTED MANUSCRIPT
1-Ethoxycarbonylmethyl-5-phenyl-3-(p-methoxyphenyl)-3H-imidazol-1-ium bromide 5b. Yield
o
1
0.363 g, 87%. Colourless crystals, mp 195–196 C. IR (KBr) νC=O 1744 cm-1; H NMR (400 MHz,
DMSO-d6): δ 1.07 (3H, t, J = 6.8 Hz), 3.84 (3H, s), 4.08 (2H, q, J =
Ph
6.8 Hz), 5.31 (2H, s), 7.22 (2H, d, J = 9.2 Hz), 7.58 (5H, s), 7.74 (2H,
O
N
Br
N
13
d, J = 9.2 Hz), 8.53 (1H, d, J = 1.2 Hz), 9.86 (1H, d, J = 1.2 Hz). C
O
NMR (100 MHz, DMSO-d6): δ 14.2; 48.9; 56.3; 62.6; 115.8; 119.9;
123.8; 125.3; 128.0; 129.6; 129.8; 131.0; 135.6; 137.2; 160.7; 166.6.
Anal. Calcd for C20H21BrN2O3 (417.30) C, 57.56; H, 5.07; N, 6.71;
Found C, 58.00; H, 4.73; N, 7.00.
O
5b
1-(-)-Menthyloxycarbonylmethyl-5-phenyl-3-(p-tolyl)-3H-imidazol-1-ium bromide 5c. Yield 0.430
o
g, 84%. Colourless crystals, mp 171–172 C. IR (KBr) νC=O 1757 cm-1; 1H NMR (400 MHz, DMSO-
Ph
d6): δ 0.52-0.85 (12H, m), 1.23-1.63 (6H, m), 2.40 (3H, s), 4.53 (1H,
N
Br
N
dt, J = 11.2; 1.1 Hz), 5.35 (1H, d, J = 18.4 Hz), 5.41 (1H, d, J = 18.4
Hz), 7.49 (2H, d, J = 8.0 Hz), 7.56-7.58 (5H, s), 7.73 (2H, d, J = 8.0
Hz), 8.57 (1H, d, J = 1.2 Hz), 9.89 (1H, d, J = 1.2 Hz). 13C NMR (100
MHz, DMSO-d6): δ 16.5; 20.9; 21.1; 22.2; 23.2; 26.0; 31.1; 33.8;
46.6; 49.0; 76.4; 119.9; 122.0; 125.3; 129.5; 129.7; 131.0; 131.2;
132.6; 135.7; 137.3; 140.5; 166.1. Anal. Calcd for C28H35BrN2O2
(511.49) C, 65.75; H, 6.90; N, 5.48; Found C, 65.60; H, 6.66; N, 5.68.
O
O
5c
1-Carbamoylmethyl-5-phenyl-3-(p-tolyl)-3H-imidazol-1-ium chloride 5d. Yield 0.246 g, 75%.
o
1
Colourless crystals, mp 263–264 C. IR (KBr) νC=O 1691; νNH2 3244 and 3399 cm-1; H NMR (400
MHz, DMSO-d6): δ 2.40 (3H, s), 5.00 (2H, s), 7.26 (1H, brs), 7.39
Ph
(1H, brs), 7.48 (2H, d, J = 8.4 Hz), 7.57 (5H, s), 7.75 (2H, d, J = 8.4
Hz), 8.55 (1H,s), 10.17 (1H, s). 13C NMR (100 MHz, DMSO-d6):
N
Cl
N
O
δ 21.0; 49.8; 119.2; 121.7; 125.4; 129.6; 129.7; 130.9; 131.1; 132.6;
135.8; 137.4; 140.3; 166.7.
NH2
5d
Anal. Calcd for C18H18ClN3O (327.81) C, 65.95; H, 5.53; N, 12.82;
Found C, 65.50; H, 5.45; N, 12.53.
1-(N-2,6-Dimethylphenyl)carbamoylmethyl-5-phenyl-3-(p-tolyl)-3H-imidazol-1-ium chloride 5e.
11

ACCEPTED MANUSCRIPT
o
Yield 0.315 g, 73%. Colourless crystals, mp 252–253 C. IR (KBr) νC=O 1665 cm-1; νNH 3397 and
3359 cm-1 1H NMR (400 MHz, DMSO-d6): δ 1.94 (6H, s), 2.40 (3H,
Ph
s), 5.33 (2H, s), 7.01-7.03 (3H, m),7.50 (2H, d, J = 8.4 Hz), 7.59-7.63
N
Cl
N
(5H, m), 7.75 (2H, d, J = 8.4 Hz), 8.55 (1H, d, J = 1.6 Hz), 9.85 (1H,
s), 10.04 (1H, d, J = 1.6 Hz). 13C NMR (100 MHz, DMSO-d6): δ 18.3;
O
NH
21.0; 49.9; 119.4; 121.7; 125.5; 127.3; 128.2; 129.7; 129.8;
130.9;131.2; 132.6; 134.3; 135.4; 135.8; 137.5; 140.3; 163.4.
Anal. Calcd for C26H26ClN3O (431.96) C, 72.29; H, 6.07; N, 9.73;
Found C, 71.90; H, 5.85; N, 9.49.
5e
IV.3 Synthesis of Ag(I) metalated 3H-imidazol-1-ium salts 7a-e. General procedure. To a solution
of 5a-e (0.3 mmol) in CH2Cl2 (3 mL) in the presence of molecular sieve (4A, 0.300 g) Ag2O (0.15
mmol, 0.035 g) was added portion-wise within 5 min and the reaction mixture stirred for 20 min at
o
dark. The reaction mixture was filtered and the filtrate evaporated at 25 C under vacuum. The pure
compound (by 1H NMR) solidifies after standing in a vacuum oven for overnight.
5a Ag(I) complex 6a. Yield 0.149 g, 98%. Colourless crystals, mp 78–80 oC. IR (KBr) νC=O 1745
1
cm-1, H NMR (400 MHz, CDCl3): δ 1.22 (3H, t, J = 7.2 Hz), 2.41 (3H, s), 4.17 (2H, q, J = 7.2 Hz),
5.02 (2H, s), 7.23 (1H, s), 7.26-7.28 (2H, d, m), 7.37-7.39 (2H, m),
Ph
13
7.46-7.52 (5H, d, J = 8.0 Hz). C NMR (100 MHz, CDCl3): δ 14.1;
N
N
21.1; 51.0; 62.2; 119.6; 123.7; 126.9; 129.1; 129.5; 129.9; 130.4;
BrAg
O
O
136.1; 137.3; 139.1; 167.8; 182.0. Anal. Calcd for C20H20AgBrN2O2
(508.16) C, 47.27; H, 3.97; N, 5.51; Found C, 46.68; H, 3.68; N, 5.26.
6a
5b Ag(I) complex 6b. Yield 0.150 g, 96%. Colourless crystals, mp 93–95 oC. IR (KBr) νC=O 1740
1
cm-1, H NMR (400 MHz, CDCl3): δ 1.23 (3H, t, J = 7.6 Hz), 3.87 (3H, s), 4.19 (2H, q, J = 7.6 Hz),
4.94 (2H, s), 7.00 (2H, d, J = 8.4 Hz), 7.21 (1H, s), 7.37-7.39 (2H, m),
Ph
13
7.48-7.54 (5H, m). C NMR (100 MHz, CDCl3): δ 14.1; 50.9; 55.6;
O
N
N
62.3; 114.9; 125.2; 129.1; 129.5; 129.9; 132.8; 136.0; 159.9; 167.7;
182.4. Anal. Calcd for C20H20AgBrN2O3 (524.16) C, 45.83; H, 3.85;
N, 5.34; Found C, 46.05; H, 3.46; N, 5.34.
BrAg
O
O
6b
5c Ag(I) complex 6c. Yield 0.115 g, 62%. Colourless crystals, mp 88–90 oC. IR (KBr) νC=O 1741 cm-
1,1H NMR (400 MHz, CDCl3): δ 0.66 (3H, d, J = 6.4), 0.83 (3H, d, J = 7.2), 0.89 (3H, d, J = 6.4), 0.93-
1.86 (8H, m), 2.42 (3H, s), 4.68 (1H, dt, J = 10.8; 4.0 Hz), 4.94 (1H, d,
12

ACCEPTED MANUSCRIPT
Ph
J = 17.6), 5.00 (1H, d, J = 17.6), 7.23 (1H, s), 7.28-7.31 (3H, m), 7.38-
N
7.40 (2H, m), 7.46-7.52 (4H, m). 13C NMR (100 MHz, CDCl3):
δ 16.1; 20.8; 21.1; 21.9; 23.1; 26.0; 31.4; 33.9; 40.6; 46.8; 51.3; 76.5;
119.8; 121.3; 123.7; 124.9; 126.9; 128.6; 129.1; 129.9; 130.5; 136.1;
137.3; 139.2; 167.2; 183.5. Anal. Calcd for C28H34AgBrN2O2 (618.35)
C, 54.39; H, 5.54; N, 4.53; Found C, 54.34; H, 5.69; N, 4.94.
N
BrAg
O
O
6c
5d Ag(I) complex 6d. Yield 0.050 g, 40%. Colourless crystals, mp 124-125 oC. IR (KBr) νNH2 3328
and 3177 cm-1; νC=O 1686 ,1H NMR (400 MHz, CDCl3): δ 2.41 (3H, s), 5.19 (2H, s), 5.72 (1H, br s),
7.10 (2H, d, J = 8.4 Hz), 7.19 (1H, s), 7.35 (2H, d, J = 8.4 Hz), 7.45-
Ph
13
N
7.49 (5H, m), 8.98 (1H, brs). C NMR (100 MHz, CDCl3): δ 21.1;
N
ClAg
29.7 51.4; 118.8; 123.6; 126.9; 129.0; 129.6; 129.9; 130.1; 137.4;
137.5; 138.7; 169.8. Anal. Calcd for C18H17AgClN3O (434.67) C,
49.74; H, 3.94; N, 9.67; Found C, 50.01; H, 3.56; N, 9.78.
O
NH2
6d
5e Ag(I) complex 6e. Yield 0.108 g, 67%. Colourless crystals, mp 158–159 oC. IR (KBr) νNH 3394
1
cm-1; νC=O 1691, H NMR (400 MHz, CDCl3): δ 2.22 (6H, s), 2.42 (3H, s), 5.29 and 5.84 (2H, 2Xs),
6.96-7.02 (3H, m), 7.10 (2H, d, J = 8.4 Hz), 7.20 (1H, s), 7.1 (2H, d, J
= 8.4 Hz), 7.42-7.46 (3H, m), 7.58-7.60 (2H, m), 10.71 (1H, br s). 13C
Ph
N
N
NMR (100 MHz, CDCl3): δ 19.0; 21.1; 51.7; 118.5; 123.6; 126.8;
ClAg
O
126.9; 127.9; 128.9; 129.8; 129.9; 130.1; 134.1; 135.3; 137.5; 138.8;
166.4. Anal. Calcd for C26H25AgClN3O (538.82) C, 57.96; H, 4.68;
N, 7.80; Found C, 58.00; H, 5.08; N, 7.90.
NH
6e
IV.4 Synthesis of Ag(I) metalated 3H-imidazol-1-ium salts 7a-e. General procedure. To a solution
of 3a-e (0.15 mmol) in CH2Cl2 (25 mL) AgNO3 (0.263 mmol, 0.044 g) and Et3N (10.8 mmol, 1.095 g,
1.5 mL, 0.73 kg/L) were added successively and the reaction mixture stirred for 2 h at dark. The
reaction mixture was washed with water (25 mL) and the organic phase separated and dried over
Na2SO4. The solvent was evaporated and the residual solid was dried under vacuum at dark.
5a Ag(I) complex 7a. Yield 0.062 g, 84%. Colourless crystals, mp 78–80 oC (decomp). IR (KBr) νC=O
1
1747 cm-1, H NMR (400 MHz, DMSO-d6): δ 1.02 (3H, t, J = 7.6 Hz), 2.36 (3H, s), 4.01 (2H, q, J =
7.6 Hz), 5.18 (2H, s), 7.29 (2H, d, J = 8.0 Hz), 7.48-7.51 (5H, m), 7.61
Ph
13
(2H, d, J = 8.0 Hz), 8.04 (1H, s). C NMR (100 MHz, DMSO-d6):
N
N
O3NAg
13
O
O
7a

ACCEPTED MANUSCRIPT
δ 14.2; 21.0; 51.4; 61.9; 121.2; 123.9; 127.5; 129.5 (2C); 130.0;
130.5; 136.1; 135.5; 138.9; 168.2 (C-Ag is not observed). Anal. Calcd
for C20H20AgN3O5 (490.26) C, 49.00; H, 4.11; N, 8.57; Found C,
49.15; H, 4.17; N, 8.70.
5b Ag(I) complex 7b. Yield 0.067 g, 88%. Colourless crystals, mp 93–95 oC (decomp). IR (KBr) νC=O
1
1747 cm-1. H NMR (400 MHz, DMSO-d6): δ 1.03 (3H, t, J = 7.6 Hz), 3.81 (3H, s), 4.01 (2H, q, J =
7.6 Hz), 5.17 (2H, s), 7.04 (2H, d, J = 8.4 Hz), 7.48-7.51 (5H, s), 7.65
13
(2H, d, J = 8.4 Hz), 7.99 (1H, S). C NMR (100 MHz, DMSO-d6):
δ 14.2; 46.2; 51.4; 56.0; 61.9; 115.2; 121.4; 123.8; 125.5; 127.5;
129.5; 133.0; 135.9; 159.8; 168.3 (C-Ag is not observed). Anal. Calcd
for C20H20AgN3O6 (506.26) C, 47.45; H, 3.98; N, 8.30; Found C,
47.55; H, 4.15; N, 8.25.
Ph
O
N
N
O3NAg
O
O
7b
5c Ag(I) complex 7c. Yield 0.072 g, 80%. Colourless crystals, mp 88–90 oC (decomp). IR (KBr) νC=O
1
1743 cm-1. H NMR (400 MHz, DMSO-d6): δ 0.49-0.94 (12H, m), 1.18-1.64 (6H, m), 2.38 (3H, s),
4.49 (1H, dt, J = 10.8; 4.0 Hz), 5.21 (2H, s), 7.33 (2H, d, J = 7.6 Hz),
Ph
13
7.50 (5H, s), 7.61 (2H, d, J = 7.6 Hz), 8.03 (1H, s). C NMR (100
N
N
MHz, DMSO-d6): δ 16.5; 20.9; 21.1; 22.2; 23.2; 26.0; 31.1; 33.9;
O3NAg
O
46.2; 46.8; 51.5; 75.6; 121.3; 122.0; 123.9; 127.4; 129.4; 129.5; 130.6;
137.6; 138.9; 167.7 (C-Ag is not observed). Anal. Calcd for
C28H34AgN3O5 (600.45) C, 56.01; H, 5.71; N, 7.00; Found C, 56.11;
H, 5.85; N, 7.10.
O
7c
5d Ag(I) complex 7d. Yield 0.054 g, 78%. Colourless crystals, mp 124-125 oC (decomp). IR
(KBr) νNH2 3370 and 3334 cm-1; νC=O 1688 cm-1. 1H NMR (400 MHz, DMSO-d6): δ 2.36 (3H, s), 4.82
(2H, s), 7.31 (2H, d, J = 8.0 Hz), 7.36 (1H, brs), 7.47-7.54 (5H, m),
7.57 (5H, s), 7.60 (2H, d, J = 8.0 Hz), 7.63 (1H, brs), 7.99 (1H,s). 13C
Ph
N
N
NMR (100 MHz, DMSO-d6): δ 21.0; 52.0; 120.8; 123.7; 127.7; 129.4;
O3NAg
129.5; 129.9; 130.6; 136.3; 137.6; 138.8; 168.7 (C-Ag is not
O
NH2
7d
observed). Anal. Calcd for C18H17AgN4O4 (461.22) C, 46.87; H, 3.72;
N, 12.15; Found C, 46.95; H, 3.50; N, 11.95.
5e Ag(I) complex 7e. Yield 0.073 g, 86%. Colourless crystals, mp 158–159 oC (decomp). IR
14

ACCEPTED MANUSCRIPT
(KBr) νNH 3443; νC=O 1696 cm-1. 1H NMR (400 MHz, DMSO-d6): δ 1.86 (6H, s), 2.30 (3H, s), 5.20
(2H, s), 6.97-7.01 (3H, m), 7.29 (2H, d, J = 7.2 Hz), 7.53-7.55 (5H,
Ph
13
N
m), 7.62 (2H, d, J = 7.2 Hz), 8.03 (1H, s), 9.53 (1H, brs). C NMR
(100 MHz, DMSO-d6): δ 18.3; 21.0; 46.2; 121.8; 123.7; 127.1; 127.7;
128.1; 129.5; 129.7; 130.6; 131.2; 134.6; 135.4; 136.3; 137.6; 138.9;
165.3 (C-Ag is not observed). Anal. Calcd for C26H25AgN4O4
(565.37) C, 55.23; H, 4.46; N, 9.91; Found C, 55.35; H, 4.60; N,
10.10.
N
O3NAg
O
NH
7e
IV.5 Synthesis of 3H-imidazol-1-ium 2-yliden Pd (II) complexes 8a-e. Method A. General
Procedure. To a solution of Ag(I) complexes 6a-e (0.25 mmol) in CH2Cl2 (5 mL) Pd(CH3CN)2Cl2
(0.25 mmol, 0.065 g,) was added and the reaction mixture stirred for 20 min at dark. The precipitated
AgX was removed by filtration through a celite bed. The solvent of the filtrate was evaporated under
reduced pressure at room temperature. The formed orange coloured solids were dried under vacuum.
5a Pd(II) complex 8a. Yield, 0.116 g, 93%. Orange powder. Mp 183–186 oC (decomp). IR (KBr) νC=O
1
1744 cm-1; H NMR (400 MHz, DMSO-d6): δ 1.14 (3H, t, J = 7.6 Hz), 2.44 (3H, s), 4.14 (2H, q, J =
7.6 Hz), 5.27 (1H, d, J = 18.0 Hz), 5.60 (1H, d, J = 18.0 Hz), 7.43-7.53
Ph
13
N
(7H, m), 7.95 (2H, d, J = 8.4 Hz), 8.04 (1H, s). C NMR (100 MHz,
N
Cl
CDCl3): 14.1; 21.3; 50.2; 62.4; 121.5; 125.5; 126.6; 129.0; 129.1;
Pd
O
Cl
13
O
129.7; 130.0; 130.3; 130.6; 135.9; 137.1; 169.3. C NMR (100 MHz,
8a
DMSO-d6): δ 14.3; 21.1; 50.3; 62.1; 122.0; 125.5; 127.1; 129.4;
129.6; 130.1; 130.4; 136.3; 136.6; 139.5; 167.8. Anal. Calcd for
C20H20Cl2N2O2Pd (497.71) C, 48.26; H, 4.05; N, 5.63; Found C,
48.38; H, 4.19; N, 5.71.
5b Pd(II) complex 8b. Yield, 0.122 g, 95%. Orange powder. Mp 115-118 oC (decomp). IR (KBr) νC=O
1
1748 cm-1; H NMR (400 MHz, DMSO-d6): δ 1.14 (3H, t, J = 7.2 Hz), 3.86 (3H, s), 4.14 (2H, q, J =
7.2 Hz), 5.26 (1H, d, J = 17.6 Hz), 5.59 (1H, d, J = 17.6 Hz), 7.27 (2H,
d, J = 9.2 Hz), 7.47-7.50 (5H, m), 7.96 (2H, d, J = 9.2 Hz), 7.99 (1H,
Ph
s). 13C NMR (100 MHz, CDCl3): δ 14.1; 50.1; 55.7; 62.5; 114.8;
121.7; 126.6; 127.2; 129.0; 129.6; 130.0; 131.4; 137.1; 145 (C-Pd);
160.1; 166.9. 13C NMR (100 MHz, DMSO-d6): δ 14.3; 50.3; 56.2;
62.1; 115.0; 126.7; 127.1; 127.2; 129.3; 129.6; 130.1; 131.6; 136.4;
O
N
N
Cl
Pd
Cl
O
O
8b
15

ACCEPTED MANUSCRIPT
160.1; 167.8. Anal. Calcd for C20H20Cl2N2O3Pd (513.71) C, 46.76; H,
3.92; N, 5.45; Found C, 46.13; H, 4.12; N, 5.55.
5c Pd(II) complex 8c. Yield 0.112 g, 92%. Orange powder. Mp 113-115 oC (decomp). IR (KBr) νC=O
1744 cm-1; 1H NMR (400 MHz, DMSO-d6): δ 0.52-1.64 (18H, m), 2.44 (3H, s), 4.53 and 4.66 (1H, 2X
dt, J = 10.8; 4.0 Hz), 5.29-5.39 (1H, m, overlapping A parts of an AB
system), 5.59-5.75 (1H, m, overlapping B parts of an AB system),
Ph
13
N
7.44-7.53 (7H, m), 7.94 (2H, d, J = 7.6 Hz), 8.03 (1H, s). C NMR
N
Cl
(100 MHz, CDCl3): 16.2; 20.9; 21.4; 21.9; 23.2; 25.9; 31.4; 34.1;
Pd
O
Cl
O
40.4; 46.9; 50.3; 76.3; 121.6; 125.7; 126.8; 128.9; 129.5; 129.9; 130.2;
130.7; 136.1; 137.0; 139.2; 141.2; 166.4. Anal. Calcd for
C28H34Cl2N2O2Pd (607.91) C, 55.32; H, 5.64; N, 4.61; Found C,
55.00; H, 5.53; N, 4.71.
8c
5d Pd(II) complex 8d. Yield 0.089 g, 76%. Orange powder. Mp 248-250 oC (decomp). IR (KBr) νNH2
1
3323.9 and 3419.8; νC=O 1687 cm-1, H NMR (400 MHz, DMSO-d6): δ 2.43 (3H, s), 4.61 (1H, d, J =
17.6 Hz), 5.54 (1H, d, J = 17.6 Hz), 7.43-7.56 (7H, m), 7.99 (2H, d, J
Ph
13
= 8.8 Hz), 8.00 (1H, s). C NMR (100 MHz, CDCl3): δ 21.2; 50.2;
117.8; 122.3; 125.5; 129.5; 130.1; 130.3; 131.0; 132.1; 134.5; 137.2;
140.8; 164.9. Anal. Calcd for C18H17Cl2N3OPd (468.67) C, 46.13; H,
3.66; N, 8.97; Found C, 46.25; H, 3.55; N, 9.00.
N
N
Cl
Pd
Cl
O
NH2
8d
5e Pd(II) complex 8e. Yield 0.134 g, 93%. Mp 294-296 oC (decomp). IR (KBr) νNH 3254; νC=O 1684
1
cm-1, H NMR (400 MHz, DMSO-d6): δ 2.16 (6H, s), 2.43 (3H, s), 4.99 (1H, d, J = 16.8 Hz), 5.91
(1H, d, J = 16.8 Hz), 7.08 (3H, s), 7.49-7.55 (7H, m), 8.00 (2H, d, J =
Ph
13
N
8.4 Hz), 8.03 (1H, s). C NMR (100 MHz, CDCl3): 18.8; 21.3; 42.8;
N
Cl
122.3; 125.6; 127.5; 127.9; 128.1; 128.4; 128.9; 129.3; 130.1; 130.2;
130.4; 133.2; 135.4; 135.5; 135.8; 137.7; 139.5; 164.4. Anal. Calcd
for C26H25Cl2N3OPd (572.82) C, 54.52; H, 4.40; N, 7.34; Found C,
54.60; H, 4.47; N, 7.60.
Pd
O
Cl
NH
8e
IV.6 Synthesis of 3H-imidazol-1-ium 2-yliden Pd (II) complexes 8a-e. Method B. General
Procedure. To a solution of Ag(I) complexes 7a-e (0.25 mmol) in CH2Cl2 (5 mL), Pd(CH3CN)2Cl2
(0.15 mmol, 0.039 g, 99%) was added and the reaction mixture stirred for 1 h at dark. The precipitated
16

ACCEPTED MANUSCRIPT
AgX was filtered through celite and the filtrate evaporated under reduced pressure at room
temperature.
Acknowledgement: Turkish Scientific and Technological Research Council (TUBİTAK) is gratefully
acknowledged for the financial support (Project No 107T840).
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Synthesis and catalytic activities of 1-alkoxycarbonyl- and 1-carbamoylmethyl-5-phenyl-3-
aryl-3H-imidazol-1-yliden-Pd(II) complexes
Meliha Çetin Korukçu and Necdet Coşkun*
1. Ag(I)
Ph 1. Pd(CH3CN)2Cl2
Ph
Ph
2. CH2Cl2
2. CH2Cl2
R
N
R
N
R
N
X
N
N
N
-H
-AgX
Cl
XAg
Pd
R1
O
O
R1
R1
O
Cl
8
5
6 (X=Br or Cl)
7 (X=NO3)
18

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4-Phenyl-1-aryl-1H-imidazoles were converted to Pd(NHC) complexes.
1-Alkoxycarbonyl-5-phenyl-3-aryl-3H-imidazol-1-yliden-Pd(II) were shown to be better catalyst than the 1-
carbamoylmethyl-5-phenyl-3-aryl-3H-imidazol-1-yliden-Pd(II) complexes.
The catalysts were shown to be insensitive to the air oxygen and water.