Synthesis, X-ray structures, and catalytic activities of (κ2-C,N)-palladacycles bearing imidazol-2-ylidenes

Article abstract of DOI:10.1016/j.jorganchem.2009.03.034

Quaternisation of methylimidazole (1) by methyl substituted benzyl bromides afforded imidazolium salts (2) which were converted to (κ²-C,N)-palladacycles bearing imidazol-2-ylidenes 6 or 7, by either in situ deprotonation or via Ag-NHC intermediate (3), using the bridged palladacycles 4 or 5, respectively. The palladacycles 6 and 7 were characterized by elemental analysis; NMR spectroscopy and the molecular structure of 6c and 7c were determined by X-ray crystallography. The complexes 6 and 7 display high activity in Suzuki-Miyaura coupling of a range of aryl bromides.

Full text of DOI:10.1016/j.jorganchem.2009.03.034

Journal of Organometallic Chemistry 694 (2009) 2343–2349
Contents lists available at ScienceDirect
Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Synthesis, X-ray structures, and catalytic activities of (
bearing imidazol-2-ylidenes
j
2-C,N)-palladacycles
a
b
b
c
M. Emin Günay a, , Rukiye Gümüßsada , Namık Özdemir , Muharrem Dinçer , Bekir Çetinkaya
*
a Department of Chemistry, Adnan Menderes University, 09010 Aydın, Turkey
b Department of Physics, Ondokuz Mayıs University, 55139, Kurupelit-Samsun, Turkey
c Department of Chemistry, Ege University, 35100 Bornova-Izmir, Turkey
a r t i c l e i n f o
a b s t r a c t
Article history:
Quaternisation of methylimidazole (1) by methyl substituted benzyl bromides afforded imidazolium
salts (2) which were converted to (
2-C,N)-palladacycles bearing imidazol-2-ylidenes 6 or 7, by either
in situ deprotonation or via Ag–NHC intermediate (3), using the bridged palladacycles 4 or 5, respectively.
The palladacycles 6 and 7 were characterized by elemental analysis; NMR spectroscopy and the molec-
ular structure of 6c and 7c were determined by X-ray crystallography. The complexes 6 and 7 display
high activity in Suzuki–Miyaura coupling of a range of aryl bromides.
Received 18 February 2009
Received in revised form 18 March 2009
Accepted 19 March 2009
j
Available online 27 March 2009
Keywords:
Palladacycles
Ó 2009 Elsevier B.V. All rights reserved.
N-heterocyclic carbene
Imidazol-2-ylidenes
Suzuki–Miyaura coupling
1. Introduction
easily synthesized from commercially available heterocycles. In
contrast to the numerous known coordination complexes of N-
Cyclopalladacycles received much attention for more than
40 years in coordination- and organometallic chemistry due to
their specific structure, stability, and their role in various catalytic
reactions [1–3]. Significant efforts have been devoted in derivatiz-
ing the basic skeletons in order to improve and tune their catalytic
properties. Their electronic and steric properties are influenced by
various factors, such as the size of the metallocyclic ring, the type
of the donor atoms, and the nature of the co-ligands. In this con-
text, palladacyclic complexes, derived from organic molecules
bearing N-donor groups, have played a significant role that can
operate at very low metal loadings [4]. Apparently palladacyclic
catalysts alone are helpless and the modulation of activity of Pd
catalyst by the co-ligands is required, e.g. in the case of unactivated
aryl chlorides, as well as the reactions of aryl bromides at lower
temperatures [5–10]. An interesting approach is to combine palla-
dacycles as convenient Pd sources and special ligands in catalytic
system, e.g. NHC ligands, and to use preformed 1:1 complex. These
complexes are air stable, and thus are more convenient in handling
than toxic phosphines derivatives [5].
benzyl substituted NHC’s, the number of their cyclopalladated
derivatives remain limited [16,17]. Therefore, the main aim of this
study is to investigate the effect of sp2 vs. sp3 hybridized N’s of the
5-membered palladacyclic ring.
2. Results and discussion
2.1. Preparation of ligands
The general route to the target NHC ligand precursors and pal-
ladacyclic complexes is shown in Scheme 1. Unsymmetrical imi-
dazolium salts 2a–c were synthesized by the reaction of 1 with
2,4,6-trimethylbenzyl, 2,3,5,6-tetramethylbenzyl or 2,3,4,5,6-pen-
tamethylbenzyl bromides. The salts 2a–c could be purified by
recrystallization from ethanol and by addition of diethyl ether.
The NMR spectroscopic data of 2a–c agree with the proposed
structures. In the 1H NMR spectra of 2a–c, the imidazolium protons
appear at d 10.16, 10.02, and 9.94 ppm, respectively. The 13C NMR
shift of the NCN sp2 carbon atoms in 2a–c appear between d 140.1
and 137.5 ppm, respectively. Signals at d 48.1–49.3 ppm corre-
spond to the benzylic methylene carbon resonances for 2a–c.
NHC’s have attracted our attention because a variety of N-ben-
zyl-substituted NHC-based metal complexes have been found to
exhibit high efficiency in various C–C bond forming reactions cat-
alyzed by palladium [11–15]. Also, these ligand precursors can be
2.2. Synthesis of silver(I)–NHC and palladacyclic complexes
We prepared mononuclear palladacyclic NHC complexes from
salts 2 by in situ deprotonation or via AgNHC complexes (3). Reac-
* Corresponding author. Tel.: +90 256 212 8498; fax: +90 256 213 5379.
E-mail address: megunay@adu.edu.tr (M. Emin Günay).
0022-328X/$ - see front matter Ó 2009 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2009.03.034

2344
M. Emin Günay et al. / Journal of Organometallic Chemistry 694 (2009) 2343–2349
CH3
N
a
c
b
N
1
Ar
Br
(i)
Ar
H3C
CH3
N
N
N
CH3
N
N
Pd Cl
(iii)
(ii)
(iv)
H Br-
AgBr2
Pd
+
)
N
2
Ag
)
2
Ar
Br
N
N
N
CH3
N
Ar
Ar
Ar
3
7a-c
6a-c
2
OAc
2
N
Pd
Pd Cl
N
2
4
5
Scheme 1. Reagents and conditions: (i) PhMe, 25 °C; (ii) Ag2O, CH2Cl2, 25 °C; (iii) 4, PhMe, 110 °C; (iv) 5, CH2Cl2, 25 °C.
tions of the imidazolium precursors with palladium dimer [Pd-
-OAc)(ppy)]2 (ppy: 2-phenylpyridine), (4) in toluene at 110 °C
(l
gave the palladacyclic complexes 6a–c in moderate yields. On the
other hand, Pd analogs 7a–c were synthesized by a transmetalla-
tion reaction between [Pd(dmba)(l-Cl)]2 (dmba: dimethylbenzyl-
amine), (5) and the Ag-containing carbenes 3a–c (Scheme 1) in
CH2Cl2 at 25 °C. Since silver(I)–NHC complexes are easy to make
and can be used as air-moisture-stable carbene transfer agent
[18–23].
Solutions of complexes 6a–c and 7a–c in chlorinated solvents
were observed to be stable toward air and moisture. The identities
of the compounds were confirmed by 1H and 13C NMR spectros-
copy and elemental analysis. All of the palladacyclic complexes ex-
hibit characteristic 13C chemical shifts which provide a useful
diagnostic tool for metal carbene complexes. The chemical shifts
for the carbene carbon atom (6, 7) fall in the range d 171.8–
173.5 ppm.
Fig. 1. A view of the complex (6c), showing 40% probability displacement ellipsoids
and the atom-numbering scheme.
In the 13C NMR spectra of 7, the chemical shifts of the carbene
carbon atoms of the Pd–NHC complexes appear at d ꢀ 182 ppm,
which is consistent with the chemical shifts of known Pd–NHC
complexes [24].
Table 1
0
Selected bond lengths (ÅA) and angles (°) for 6c.
Bond lengths (Å)
Pd1–C12
Pd1–C11
Pd1–N1
Pd1–Br1
N1–C1
N2–C5
N2–C12
1.971 (3)
1.980 (3)
2.084 (2)
2.5108 (4)
1.336 (4)
1.347 (4)
1.352 (3)
N2–C14
N2–C13
N3–C12
N3–C15
N3–C16
C14-C15
C16-C17
1.370 (4)
1.453 (4)
1.345 (4)
1.384 (4)
1.479 (4)
1.334 (4)
1.512 (5)
2.3. Structural description of 6c and 7c
The structure of the complex 6c is shown in Fig. 1 and selected
geometric parameters are listed in Table 1. The title complex con-
tains a phenylpyridine (ppy) ligand, with a PdII metal centre, a 1-
methyl-3-(2,3,4,5,6-pentamethylbenzyl)-2,3-dihydro-1H-imidazole
ligand, and one bromine ligand. The coordination around the PdII
ion is distorted cis-square-planar, and the PdII ion is coordinated
by one pyridine N atom and one aryl C atom from the bidentate
ligand, one carbenic C atom from the monodentate ligand, and
one Br atom.
The two Pd–C bond distances are almost equal in magnitude
[Pd1–C12 = 1.971(3) Å and Pd1–C11 = 1.980(3) Å] and the Pd1–
C12 bond distance is comparable to those in other palladium(II)–
NHC complexes [25–27]. The plane of the carbene ring is approxi-
mately orthogonal to the square plane [84.32(9)°] The bonding
within the N-heterocyclic carbene (NHC) ring indicates a pattern
Bond angles (°)
C12–Pd1–C11
C12–Pd1–N1
C11–Pd1–N1
C12–Pd1–Br1
C11–Pd1–Br1
N1–Pd1–Br1
C12–N2–C14
C12–N2–C13
C14–N2–C13
91.15 (10)
172.46 (10)
81.30 (10)
90.84 (7)
175.27 (8)
96.68 (6)
110.5 (2)
123.9 (2)
125.5 (2)
C12–N3–C15
C12–N3–C16
C15–N3–C16
N3–C12–N2
N3–C12–Pd1
N2–C12–Pd1
C15–C14–N2
C15–C14–N3
N3–C16–C17
110.6 (2)
123.5 (2)
125.8 (3)
104.9 (2)
129.6 (2)
125.5 (2)
107.4 (2)
106.5 (3)
112.5 (3)
of delocalization that extends from atom N2 to atom N3 through
atom C12, the N2–C12 [1.352(3) Å] and N3–C12 [1.345(4) Å] dis-
tances being significantly shorter than the N2–C14 [1.370(4) Å]

M. Emin Günay et al. / Journal of Organometallic Chemistry 694 (2009) 2343–2349
2345
and N3–C15 [1.384(4) Å] distances as is in similar NHC transition
metal complexes [28–30].
into the formally empty p(
C1 and C12) [33,34].
p) orbital on the carbene C atom (herein
The structure of the complex 7c is shown in Fig. 2 and selected
geometric parameters are listed in Table 2. The complex contains a
N,N-dimethyl-1-phenylmethanamine ligand, with a PdII metal cen-
tre, a 1-methyl-3-(2,3,4,5,6-pentamethyl-benzyl)-2,3-dihydro-1H-
imidazol-2-ylidene ligand, and one chlorine ligand. The coordina-
tion around the PdII ion is distorted cis-square-planar, and the PdII
ion is coordinated by one amine N atom and one aryl C atom from
the bidentate ligand, one carbenic C atom from the monodentate
ligand, and one Cl atom.
The plane of the carbene ring is approximately orthogonal to
the square plane 73.12(10), while the plane of the C17–C22 ben-
zene ring is almost coplanar with the square plane 13.57(13). Sim-
ilarly to the complex 6c, the bonding within the N-heterocyclic
carbene (NHC) ring indicates a pattern of delocalization that ex-
tends from atom N1 to atom N2 through atom C1, the N1–C1
[1.348(4) Å] and N2–C1 [1.350(4) Å] distances being significantly
shorter than the N1–C2 [1.383(4) Å] and N2–C3 [1.387(4) Å] dis-
tances. These observations in complex 6c and 7c are possibly indic-
ative of a greater partial double-bond character due to partial
electron donation by nitrogen to the carbene C-atom donor
[31,32]. Theoretical studies also indicate that the stability of these
carbenes is due to electron donation from the N-atom lone pairs
The two coordinated C atoms in both complexes are cis to each
other, which is in agreement with the fact that the donor groups
with the largest trans influence avoid being mutually trans to
one another. The change in geometrical parameters due to the dif-
ference of the bidentate ligand, does seem to significantly affect
the coordination to the palladium(II) centre (Tables 1 and 2).
Although the two Pd–C distances in both complex are in same
magnitude, the Pd–N bond distances are significantly different.
The Pd–N bond in complex 6c is shorter than that in complex 7c.
It can be inferred from this result that the trans influence of
carbene C atom in complex 7c is larger than that in complex 6c.
However, the bite angle is not affected by the difference of the
bidentate ligand and remains nearly constant. The difference be-
tween the Pd–N bond distances in both complexes can also be
attributed to the different hybridization of the Nsp2 and Nsp3
atoms. The single-crystal data and X-ray collection parameters
are given in Table 3.
2.4. Catalytic studies
Since its discovery in 1979 [35], the Suzuki–Miyaura reaction is
one of the most important transformations leading to the construc-
tion of unsymmetrical biphenyls. Pioneering work in the use of pal-
ladacycles for the Suzuki–Miyaura reaction was performed by
Herrmann and co-workers using a phosphine-bearing palladacycle
in the coupling reaction [36]. Good activity is not limited to phos-
phines donor systems because N-donor palladacycles have also
been described with good results [37,38]. A preliminary Suzuki
reaction was then conducted in the presence of palladacyclic com-
plexes 6 and 7. The coupling of aryl bromides with phenylboronic
acid in 2-propanol with 1 mol% catalyst loading, and a reaction
Table 3
Summary of X-ray crystallographic data for complex 6c and 7c.
Parameter
6c
7c
Empirical formula
Crystal size (mm)
Mr
C27H30BrN3Pd
0.47 ꢁ 0.42 ꢁ 0.38
582.85
C25H34ClN3Pd
0.65 ꢁ 0.37 ꢁ 0.09
518.43
296
0.71073
Fig. 2. A view of the complex (7c), showing 40% probability displacement ellipsoids
and the atom-numbering scheme.
T (K)
296
Wavelength (Å)
Crystal system
Space group
a (Å)
b (Å)
c (Å)
0.71073
Monoclinic
C2/c
27.5032 (9)
9.1670 (3)
19.6139 (7)
90
96.876 (3)
90
4909.5 (3)
8
Triclinic
ꢀ
P1
Table 2
9.1975 (3)
10.1400 (4)
12.8922 (5)
90.728 (3)
91.709 (4)
91.728 (3)
1201.17 (8)
2
1.433
0.90
1.58–27.57
ꢂ11 6 h 6 11,
0
Selected bond lengths (ÅA) and angles (°) for 7c.
Bond Lengths [Å]
a
(°)
Pd1–C1
1.973 (3)
1.973 (3)
2.147 (2)
2.4360 (8)
1.348 (4)
1.383 (4)
1.449 (4)
1.350 (4)
N2–C3
N2–C5
N3–C25
N3–C23
N3–C24
C2-C3
1.387 (4)
1.477 (4)
1.466 (4)
1.488 (4)
1.467 (4)
1.331 (5)
1.507 (4)
1.487 (5)
b (°)
Pd1–C17
Pd1–N3
Pd1–Cl1
N1–C1
N1–C2
N1–C4
c
(°)
V (Å3)
Z
qcalcd (Mg/m3)
1.577
2.40
l
(mmꢂ1
)
C5-C6
C22-C23
h Range (°)
1.49–26.78
ꢂ34 6 h 6 34,
N2–C1
_
Index ranges
Bond Angles [deg]
ꢂ11 6 k 6 11, ꢂ24 6 l 6 24 ꢂ13 6 k 6 13, ꢂ16 6 l 6 16
Number of observed
reflections
Number of
independent
reflections
Number of parameters 289
17 280
28321
C1–Pd1–C17
C1–Pd1–N3
C17–Pd1–N3
C1–Pd1–Cl1
C17–Pd1–Cl1
N3–Pd1–Cl1
C25–N3–C23
C25–N3–C24
C23–N3–C24
C25–N3–Pd1
C23–N3–Pd1
C24–N3–Pd1
91.86 (12)
174.40 (10)
82.54 (11)
91.31 (9)
176.56 (9)
94.28 (7)
109.6 (3)
109.0 (3)
109.5 (3)
107.8 (2)
105.07 (18)
115.8 (2)
C1–N1–C2
C1–N1–C4
C2–N1–C4
C1–N2–C3
C1–N2–C5
C3–N2–C5
N2–C1–N1
N2–C1–Pd1
N1–C1–Pd1
C3–C2–N1
C2–C3–N2
N2–C5–C6
110.8 (3)
124.3 (3)
124.9 (3)
110.2 (2)
123.7 (3)
126.0 (3)
105.0 (2)
127.7 (2)
127.4 (2)
106.7 (3)
107.3 (3)
114.0 (3)
5222
5532
280
1.059
Goodness-of-fit (GOF)
1.040
on F2
max/min
D
q
(e Åꢂ3
)
0.45, ꢂ0.64
0.08, ꢂ0.02
R, wR (observed data)a 0.0323, 0.0749
0.0356, 0.1035
0.0402, 0.1064
R, wR (all data)a
0.0418, 0.0781
a
Refinement method, full-matrix least squares on F2.

2346
M. Emin Günay et al. / Journal of Organometallic Chemistry 694 (2009) 2343–2349
Table 4
Suzuki–Miyaura cross-coupling reactions with aryl halides. Optimization of reaction parameter.a
6, 7 (1 mol%)
Cs2CO3 , IPA, 800C, 30 min
+
R
B(OH)2
R
Br
b,c
Entry
Pd–NHC
R
Yield (%)
1
2
3
4
5
6
7
8
6a
6a
6a
6b
6b
6b
6c
6c
6c
7a
7a
7a
7b
7b
7b
7c
7c
7c
H
Me
CH3(O)C
H
Me
CH3(O)C
H
Me
CH3(O)C
H
Me
CH3(O)C
H
Me
CH3(O)C
H
Me
96
81
88
99
84
91
99
83
92
50
68
89
99
62
94
85
67
93
9
10
11
12
13
14
15
16
17
18
CH3(O)C
a
Reagents: an aryl halide (0.50 mmol), PhB(OH)2 (0.75 mmol), Cs2CO3 (1.50 mmol), diethyleneglicol di-n-butyl ether (0.3 mmol, internal standard), palladacyclic catalyst
(1 mol%), and 2-propanol (3 mL).
b
Yields based on the aryl halide and average of two runs.
All reactions were monitored by GC.
c
time of 30 min was chosen as a standard test reaction. The
couplings occurred readily with 6a–c and 7a–c using Cs2CO3 as a
base. The results summarized in Table 4 indicate that NHC-bearing
palladacyclic complexes exhibit excellent activity at low catalyst
loadings when aryl bromides, both activated and unactivated are
used as substrates. Generally 6 are more effective than 7. This
difference may be due to stability of palladacycle in complex 6
relative to 7. Alteration of the benzyl substituent of the NHC ligand
has not shown a strong influence on the catalytic performance of
the derived catalyst. However, as the number of methyl group
increases on the benzyl substituent, the efficiency slightly
increases.
Aryl bromide substrates have shown different reactivities under
similar conditions. For example, complex 6 was found to be highly
active in the C–C coupling of phenyl bromide and phenylboronic
acid, giving almost quantitative conversions (entries 1, 4 and 7).
In contrast to the literature reports and expectations, the reaction
of activated substrate, p-bromoacetophenone, was slightly more
difficult (entries 3, 6 and 9). The reason for this difference is not
clear at this stage.
4. Experimental
4.1. General procedures
All reactions for the preparations of 6a–c and 7a–c were carried
out under argon in flame-dried glassware using standard Schlenk-
type flask. Solvents were dried and freshly distilled prior to use. All
other chemicals were used as received. 1-Methylimidazole (1) was
purchased from Merck. Palladium dimers 4 and 5 were also pre-
pared according to the literature, respectively [39,40]. 1H and 13C
NMR measurements were performed using a Varian Mercury AS
400 spectrometer operating at 400 and 100 MHz, respectively. Cat-
alytic studies were analyzed using a gas chromatograph (HP, Agi-
lant-6890N). Chemical shifts (d) are relative to TMS. Melting
points were measured in open capillary tubes with an Electrother-
mal-9200 melting point apparatus. Elemental analyses were per-
formed by TUBITAK (Ankara, Turkey) Microlab.
4.2. General procedure for the preparation of 2
The benzyl bromide derivative [41] (20 mmol) and 1-methylim-
idazole (1.6 mL, 20 mmol) were stirred in toluene (15 mL) for 3 h at
room temperature. The volume of the solution was reduced to
5 mL, diethyl ether was added to the remaining solution, which
was vigorously shaken and then decantated. The solid residue
was washed with diethyl ether (3 ꢁ 20 mL) to obtain a white solid,
which was recrystallized from ethanol/diethyl ether (3 mL/15 mL).
3. Conclusion
Facile synthesis and characterization of six new NHC complexes
incorporating (j
2-C,N)-palladacyclic frame (6a–c and 7a–c) have
been reported. The identity of 6c and 7c has been confirmed by
X-ray diffraction studies and Ccarb is found to be in trans configura-
tion to N atom. Preliminary catalytic study revealed that the new
complexes are active in the Suzuki–Miyaura cross-coupling reac-
tions with aryl bromides. It is of interest that the 2-phenylpyridine
derived palladacycle (6) exhibited higher catalytic activity than the
N,N-dimethylbenzylamine derived palladacycle (7) under the same
conditions. This difference may be due to the stability of 5-mem-
bered ring of the palladacycle in 6. The efficiency also slightly de-
pends on the NHC ligand and increases as the number of Me groups
on the benzyl substituent increases on N3 atom.
4.2.1. Compound 2a
Yield: 5.37 g, 91%, m.p.: 117–118 °C. 1H NMR (d, CDCl3): 2.26 [s,
6H, C6H2(CH3)3]; 2.38 [s, 3H, C6H2(CH3)3]; 4.10 [s, 3H, NCH3]; 5.53
[s, 2H, NCH2C6H2(CH3)3]; 6.87 [d, 1H, J = 1.6 Hz, NCHCHNCH3]; 6.90
[s, 2H, C6H2(CH3)3]; 7.46 [d, 1H, J = 1.6 Hz, NCHCHNCH3]; 10.16 [s,
1H, NCHN]. 13C NMR (d, CDCl3): 20.0 [C6H2(CH3)3]; 21.2
[C6H2(CH3)3]; 37.2 [NCH3]; 48.1 [NCH2C6H2(CH3)3]; 120.9
[NCHCHNCH3]; 124.0 [NCHCHNCH3]; 125.5, 130.1, 137.0, 138.3
[C6H2(CH3)3]; 140.1 [NCHN].

M. Emin Günay et al. / Journal of Organometallic Chemistry 694 (2009) 2343–2349
2347
4.2.2. Compound 2b
(2 mL) and recrystallization from dichloromethane/diethyl ether
Yield: 5.13 g, 83%, m.p.: 123–125 °C. 1H NMR (d, CDCl3): 2.16 [s,
6H, C6H(CH3)4]; 2.21 [s, 6H, C6H(CH3)4]; 4.09 [s, 3H, NCH3]; 5.59 [s,
2H, NCH2C6H(CH3)4]; 6.90 [d, 1H, J = 1.6 Hz, NCHCHN]; 7.01 [s, 1H,
C6H(CH3)4]; 7.51 [d, 1H, J = 1.6 Hz, NCHCHN]; 10.02 [s, 1H, NCHN].
13C NMR (d, CDCl3): 16.1 [C6H(CH3)4]; 20.6 [C6H(CH3)4]; 37.3
[NCH3]; 48.8 [NCH2C6H(CH3)4]; 121.1 [NCHCHNCH3]; 123.8
[NCHCHNCH3]; 128.1, 133.8, 134.3, 135.2 [C6H(CH3)4]; 137.2
[NCHN].
afforded the complexes of type 6 (2 mL/10 mL).
4.4.2. Preparation of complexes 7
A 50 mL Schlenk tube was charged with silver compound, 3
(0.46 mmol), [Pd(dmba)(l-Cl)]2 (0.150 g, 0.27 mmol) and 10 mL
of CH2Cl2. The reaction mixture was stirred at room temperature
for 24 h. The resulting solution was then filtered and recrystallized
from dichloromethane/diethyl ether to give as a white solid.
4.4.3. Compound 6a
4.2.3. Compound 2c
Yield: 0.072 g, 55%, m.p.: 196–198 °C. 1H NMR (d, CDCl3): 2.24
[s, 6H, C6H2(CH3)3]; 2.28 [s, 3H, C6H2(CH3)3]; 3.98 [s, 3H, NCH3];
5.36 [d, 1H, J = 16 Hz, NCHCHNCH3]; 5.69 [d, 1H, J = 16 Hz,
NCHCHNCH3]; 6.18 [d, 1H, J = 8.0 Hz, pyridyl-CH]; 6.39 [s, 2H,
NCH2C6H2(CH3)3]; 6.89 [s, 2H, C6H2(CH3)3]; 6.94 [t, 1H, J = 8.0 Hz,
pyridyl-CH]; 7.10 [t, 1H, J = 8.0 Hz, pyridyl-CH]; 7.22 [t, 1H,
J = 8.0 Hz, pyridyl-CH]; 7.59 [d, 1H, J = 8.0 Hz, pyridyl-CH]; 7.73
[d, 1H, J = 8.0 Hz, pyridyl-CH]; 7.81 [t, 1H, J = 8.0 Hz, pyridyl-CH];
9.54 [d, 1H, J = 8.0 Hz, pyridyl-CH]. 13C NMR (d, CDCl3): 20.2
Yield: 6.08 g, 94%, m.p.: 192–194 °C. 1H NMR (d, CDCl3): 2.17 [s,
6H, C6(CH3)5]; 2.18 [s, 6H, C6(CH3)5]; 2.21 [s, 3H, C6(CH3)5]; 4.08 [s,
3H, NCH3]; 5.57 [s, 2H, NCH2C6(CH3)5]; 6.91 [d, 1H, J = 1.6 Hz,
NCHCHNCH3]; 7.54 [d, 1H, J = 1.6 Hz, NCHCHNCH3]; 9.94 [s, 1H,
NCHN]. 13C NMR (d, CDCl3): 17.0 [C6(CH3)5]; 17.1 [C6(CH3)5]; 17.4
[C6(CH3)5];
37.2
[NCH3];
49.3
[NCH2C6(CH3)5];
121.1
[NCHCHNCH3]; 123.9 [NCHCHNCH3]; 125.4, 133.8, 133.9, 136.9
[C6(CH3)5]; 137.5 [NCHN].
[C6H2(CH3)3];
21.2
[C6H2(CH3)3];
38.9
[NCH3];
49.7
4.3. Preparation of Ag–NHC complexes 3a–c
[NCH2C6H2(CH3)3]; 118.3 [NCHCHNCH3)]; 119.5 [Ar-C]; 121.6
[NCHCHNCH3)]; 122.6, 124.1, 124.4, 127.9, 129.5, 129.9, 136.4,
138.6, 138.7, 138.8, 146.9, 151.4, 155.7, 164.5 [Ar–C]; 173.5 [Pd–
Ccarbene]. Anal. Calc. for C25H26BrN3Pd (554.81): C, 54.12; H, 4.72;
N, 7.57. Found: C, 54.43; H, 4.26; N, 7.98%.
A suspension of 2a–c and an equivalent amount Ag2O (0.063 g,
0.27 mmol) in CH2Cl2 (15 mL) was stirred at room temperature for
8 h. The colour of the suspension gradually changed from black to
colorless. The suspension was then filtered, washed with CH2Cl2
and dried under vacuum to give a white solid. Purification was
achieved by repeated recrystallization from CH2Cl2/ether.
4.4.4. Compound 6b
Yield: 0.075 g, 54%, m.p.: 180–182 °C. 1H NMR (d, CDCl3): 2.16
[s, 6H, C6H(CH3)4]; 2.22 [s, 6H, C6H(CH3)4]; 3.98 [s, 3H, NCH3];
5.44 [d, 1H, J = 16 Hz, NCHCHNCH3]; 5.75 [d, 1H, J = 12 Hz,
NCHCHNCH3]; 6.20 [d, 1H, J = 8.0 Hz, pyridyl-CH]; 6.39 [s, 2H,
NCH2C6H(CH3)4]; 6.88 [s, 1H, C6H(CH3)4]; 6.97 [t, 1H, J = 8.0 Hz,
pyridyl-CH]; 7.10 [t, 1H, J = 8.0 Hz, pyridyl-CH]; 7.22 [t, 1H,
J = 8.0 Hz, pyridyl-CH]; 7.59 [d, 1H, J = 8.0 Hz, pyridyl-CH]; 7.74
[d, 1H, J = 8.0 Hz, pyridyl-CH]; 7.81 [t, 1H, J = 8.0 Hz, pyridyl-CH];
9.55 [d, 1H, J = 8.0 Hz, pyridyl-CH]. 13C NMR (d, CDCl3): 16.2
4.3.1. Compound 3a
Yield: 0.243 g, 71%; m.p.: 162–163 °C. 1H NMR (d, CDCl3): 2.25
[s, 12H, C6H2(CH3)3]; 2.29 [s, 6H, C6H2(CH3)3]; 3.86 [s, 6H, NCH3];
5.30 [s, 4H, NCH2C6H2(CH3)3]; 6.55 [d, 2H, J = 4.0 Hz, NCHCHNCH3];
6.91 [d, 2H, J = 4.0 Hz, NCHCHNCH3]; 6.92 [s, 4H, C6H2(CH3)3]. 13C
NMR (d, CDCl3): 20.2 [C6H2(CH3)3]; 21.2 [C6H2(CH3)3]; 39.3
[NCH3]; 49.8 [NCH2C6H2(CH3)3]; 120.1 [NCHCHNCH3]; 121.9
[NCHCHNCH3]; 127.8, 129.9, 138.0, 139.2 [Ar–C]; 182.3 [Ag–
Ccarbene].
[C6H(CH3)4];
20.6
[C6H(CH3)4];
38.9
[NCH3];
50.5
[NCH2C6H(CH3)4]; 118.3 [NCHCHNCH3]; 119.9 [Ar–C]; 121.5
[NCHCHNCH3]; 122.6, 124.0, 124.4, 129.9, 130.8, 132.5, 134.5,
134.8, 136.5, 138.6, 146.9, 151.5, 155.8, 164.5 [Ar–C]; 173.4 [Pd–
Ccarbene]. Anal. Calc. for C26H28BrN3Pd (568.84): C, 54.90; H, 4.96;
N, 7.39. Found: C, 54.75; H, 4.19; N, 7.28%.
4.3.2. Compound 3b
Yield: 0.222 g, 66%; m.p.: 157–158 °C. 1H NMR (d, CDCl3): 2.17
[s, 12H, C6H(CH3)4]; 2.25 [s, 12H, C6H(CH3)4]; 3.86 [s, 6H, NCH3];
5.36 [s, 4H, NCH2C6H(CH3)4]; 6.57 [d, 2H, J = 4.0 Hz, NCHCHNCH3];
6.90 [d, 2H, J = 4.0 Hz, NCHCHNCH3]; 7.04 [s, 2H, C6H(CH3)4]. 13C
NMR (d, CDCl3): 16.1 [C6H(CH3)4]; 20.7 [C6H(CH3)4]; 39.3 [NCH3];
50.4 [NCH2C6H(CH3)4]; 120.4 [NCHCHNCH3]; 121.8 [NCHCHNCH3];
130.6, 132.9, 134.0, 134.9 [Ar–C]; 182.2 [Ag–Ccarbene].
4.4.5. Compound 6c
Yield: 0.128 g, 70%, m.p.: 279–280 °C. 1H NMR (d, CDCl3): 2.20
[s, 12H, C6(CH3)5]; 2.25 [s, 3H, C6(CH3)5]; 3.98 [s, 3H, NCH3]; 5.44
[d, 1H, J = 16 Hz, NCHCHNCH3]; 5.75 [d, 1H, J = 12 Hz,
NCHCHNCH3]; 6.20 [d, 1H, J = 8.0 Hz, pyridyl-CH]; 6.43 [s, 2H,
NCH2C6(CH3)5]; 6.95 [t, 1H, J = 8.0 Hz; pyridyl-CH]; 7.10 [t, 1H,
J = 8.0 Hz, pyridyl-CH]; 7.22 [t, 1H, J = 8.0 Hz, pyridyl-CH]; 7.59 [d,
1H, J = 8.0 Hz, pyridyl-CH]; 7.73 [d, 1H, J = 8.0 Hz, pyridyl-CH];
7.80 [t, 1H, J = 8.0 Hz, pyridyl-CH]; 9.55 [d, 1H, J = 8.0 Hz, pyridyl-
CH]. 13C NMR (d, CDCl3): 17.0 [C6(CH3)5]; 17.2 [C6(CH3)5]; 17.3
4.3.3. Compound 3c
Yield: 0.238 g, 72%; m.p.: 148–149 °C. 1H NMR (d, CDCl3): 2.21
[s, 12H, C6(CH3)5]; 2.24 [s, 12H, C6(CH3)5]; 2.27 [s, 6H, C6(CH3)5];
3.86 [s, 6H, NCH3]; 5.36 [s, 4H, NCH2C6(CH3)5]; 6.59 [d, 2H,
J = 4.0 Hz, NCHCHNCH3]; 6.90 [d, 2H, J = 4.0 Hz, NCHCHNCH3]. 13C
NMR (d, CDCl3): 17.0 [C6(CH3)5]; 17.1 [C6(CH3)5]; 17.4 [C6(CH3)5];
39.3 [NCH3]; 50.8 [NCH2C6(CH3)5]; 120.5 [NCHCHNCH3]; 121.8
[NCHCHNCH3]; 127.8, 133.6, 133.7, 136.7 [Ar–C]; 181.9 [Ag–
Ccarbene].
[C6(CH3)5];
38.9
[NCH3];
50.9
[NCH2C6(CH3)5];
118.3
[NCHCHNCH3]; 120.1 [Ar–C]; 121.4 [NCHCHNCH3]; 122.6, 124.0,
124.4, 128.2, 129.9, 133.2, 134.4, 135.9, 136.5, 138.6, 146.9,
151.4, 155.8, 164.5 [Ar–C]; 173.2 [Pd–Ccarbene]. Anal. Calc. for
C27H30BrN3Pd (582.87): C, 55.64; H, 5.19; N, 7.21. Found: C,
55.70; H, 5.15; N, 7.10%.
4.4. General procedure for the preparation of complexes 6 and 7
4.4.1. Preparation of complexes 6
4.4.6. Compound 7a
Yield: 0.158 g, 82%, m.p.: 204–205 °C. 1H NMR (d, CDCl3): 2.23
[s, 6H, C6H2(CH3)3-o-CH3]; 2.28 [s, 3H, C6H2 (CH3)3-p-CH3]; 2.84
[s, 3H, CH2N(CH3)2]; 2.85 [s, 3H, CH2N(CH3)2]; 3.97 [s, 3H, NCH3];
5.38 [d, 1H, J = 12 Hz, NCHCHNCH3]; 5.67 [d, 1H, J = 12 Hz,
A sample of [Pd(l-OAc)2(ppy)]2 (0.150 g, 0.23 mmol) was re-
fluxed with one of the compounds of type 2 (0.46 mmol) in toluene
(10 mL) at 110 °C for 12 h. The solvent was removed in vacuo, the
remaining precipitate was then dissolved in dichloromethane

2348
M. Emin Günay et al. / Journal of Organometallic Chemistry 694 (2009) 2343–2349
NCHCHNCH3]; 6.04 [d, 1H, J = 8 Hz, C6H4]; 6.38 [s, 2H,
NCH2C6H2(CH3)3]; 6.75 [t, 1H, J = 8 Hz, C6H4]; 6.83 [s, 2H,
NCH2C6H4]; 6.88 [s, 2H, C6H2(CH3)3]; 6.95 [t, 1H, J = 8 Hz, C6H4];
7.02 [d, 1H, J = 8 Hz, C6H4]. 13C NMR (d, CDCl3): 20.2 [C6H2(CH3)3-
o-CH3]; 21.2 [C6H2(CH3)3-p-CH3]; 38.9 [NCH2C6H2(CH3)3]; 49.7
[NCH3]; 50.3 [CH2N(CH3)2]; 50.5 [CH2N(CH3)2]; 72.4 [CH2N(CH3)2];
119.5 [NCHCHNCH3]; 121.5 [NCHCHNCH3]; 122.5, 123.9, 125.7,
128.3, 129.5, 135.9, 138.6, 138.8, 148.8, 148.9 [Ar–C]; 173.1 [Pd–
Ccarbene]. Anal. Calc. for C23H30ClN3Pd (490.37): C, 56.33; H, 6.17;
N, 8.57. Found: C, 55.98; H, 5.95; N, 8.13%.
lengths at 0.96, 0.97 and 0.93 Å for CH3, CH2 and aromatic CH,
respectively. The displacement parameters of the H atoms were
constrained as Uiso(H) = 1.2Ueq (1.5Ueq for methyl) of the carrier
atom. Data collection: X-AREA [42]; cell refinement: X-AREA; data
reduction: X-RED32 [44]; molecular graphics: ORTEP-3 for Windows
[45]; software used to prepare material for publication: WINGX
[46] and PLATON [47].
Acknowledgments
Funding of our research from the TUBITAK (Project No.:
104T203) and Adnan Menderes University (Project Nos.: FEF-
07006, FEF-07013 and FBE-08001) is gratefully acknowledged.
4.4.7. Compound 7b
Yield: 0.178 g, 90%, m.p.: 205–206 °C. 1H NMR (d, 400 MHz,
CDCl3): 2.15 [s, 6H, C6H(CH3)4-o-CH3]; 2.22 [s, 6H, C6H (CH3)4-m-
CH3]; 2.85 [s, 3H, CH2N(CH3)2]; 2.86 [s, 3H, CH2N(CH3)2]; 3.98 [s,
3H, NCH3]; 5.46 [d, 1H, J = 16 Hz, NCHCHNCH3]; 5.75 [d, 1H,
J = 16 Hz, NCHCHNCH3]; 6.06 [d, 1H, J = 8 Hz, C6H2], 6.37 [s, 2H,
NCH2C6H(CH3)4]; 6.77 [t, 1H, J = 8 Hz, C6H2]; 6.81 [s, 2H, NCH2C6H4];
6.98 [t, 1H, J = 8 Hz, C6H2]; 6.99 [s, 1H, C6H(CH3)4]; 7.03 [d, 1H,
J = 8 Hz, C6H2]. 13C NMR (d, 100 MHz, CDCl3): 14.9 [C6H(CH3)4-o-
CH3]; 19.4 [C6H(CH3)4-m-CH3]; 37.7 [NCH2C6H(CH3)4]; 49.1 [NCH3];
49.2 [CH2N(CH3)2]; 71.2 [CH2N(CH3)2]; 118.5 [NCHCHNCH3]; 120.1
[NCHCHNCH3]; 121.3, 122.7, 124.5, 129.8, 131.2, 133.2, 133.6,
134.8, 147.6, 147.7 [Ar–C]; 171.8 [Pd–Ccarbene]. Anal. Calc. for
C24H32ClN3Pd (504.40): C, 57.15; H, 6.39; N, 8.33. Found: C, 56.88;
H, 6.11; N, 8.03%.
Appendix A. Supplementary data
CCDC 699017 and 699018 contain the supplementary crystallo-
graphic data for this paper. These data can be obtained free of
charge from The Cambridge Crystallographic Data Centre via
www.ccdc.cam.ac.uk/data_request/cif. Supplementary data associ-
ated with this article can be found, in the online version, at
doi:10.1016/j.jorganchem.2009.03.034.
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