Sterically hindered N-aryl/benzyl substituted piperidoimidazolin-2-ylidene palladium complexes and their catalytic activities

Article abstract of DOI:10.1016/j.tet.2018.10.003

A series of N-aryl (2a,b) or benzyl (2c,d) substituted piperidoimidazolinium salts and their palladium complexes (3a-d) were prepared and characterized by ¹H, ¹³C NMR, IR spectroscopy and elemental analysis. The crystal structures of 3a and 3c have been determined by X-ray crystallography. Thermogravimetric analysis (TGA) was applied to complexes (3a–d). The palladium complexes have been employed as catalyst for Suzuki-Miyaura cross coupling. The N-aryl substituted complex 3b was a highly efficient precatalyst and successfully employed in Suzuki-Miyaura cross coupling reactions of (hetero)aryl chlorides with arylboronic acids in air. In addition, the oxidative addition step of the reaction mechanism involving chlorobenzene and the catalysts 3a, 3b, 3c and 3d were computationally investigated by the DFT-ω-B97X-D method and complete agreement were obtained with the catalytic results. To measure σ-donating and π-acceptor properties of the new ligands, the rhodium carbonyl complexes were also prepared.

Full text of DOI:10.1016/j.tet.2018.10.003

Accepted Manuscript
Sterically hindered N-aryl/benzyl substituted piperidoimidazolin-2-ylidene palladium
complexes and their catalytic activities
Elif Gacal, Denizaltı, Armağan Kınal, Aytaç Gürhan Gökçe, Hayati Türkmen
PII:
S0040-4020(18)31176-1
10.1016/j.tet.2018.10.003
TET 29836
DOI:
Reference:
To appear in: Tetrahedron
Received Date: 26 May 2018
Revised Date: 27 September 2018
Accepted Date: 2 October 2018
Please cite this article as: Gacal E, Denizaltı , Kınal Armağ, Gökçe AytaçGü, Türkmen H, Sterically
hindered N-aryl/benzyl substituted piperidoimidazolin-2-ylidene palladium complexes and their catalytic
activities, Tetrahedron (2018), doi: https://doi.org/10.1016/j.tet.2018.10.003.
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Sterically Hindered N-Aryl/Benzyl Substituted Piperidoimidazolin-2-ylidene Complexes and
Their Catalytic Properties
Elif Gacal, Serpil Denizaltı, Armağan Kınal, Aytaç G. Gökçe, Hayati Türkmen
Department of Chemistry, Ege University, 35100 Bornova, Izmir, Turkey
Department of Physics, Dokuz Eylül University, 35160 Buca, Izmir, Turkey

1
ACCEPTED MANUSCRIPT
Tetrahedron
journal homepage: www.elsevier.com
Sterically Hindered N-Aryl/Benzyl Substituted Piperidoimidazolin-2-ylidene
Palladium Complexes and Their Catalytic Activities
a
a
a
b
a
Elif Gacal , Serpil Denizaltı , Armağan Kınal , Aytaç Gürhan Gökçe , Hayati Türkmen ,*
a
Department of Chemistry, Ege University, 35100 Bornova, Izmir, Turkey
Department of Physics, Dokuz Eylül University, 35160 Buca, Izmir, Turkey
b
ARTICLE INFO
ABSTRACT
Article history:
Received
Received in revised form
Accepted
A series of N-aryl (2a,b) or benzyl (2c,d) substituted piperidoimidazolinium salts and their
1 13
palladium complexes (3a-d) were prepared and characterized by H, C NMR, IR spectroscopy
and elemental analysis. The crystal structures of 3a and 3c have been determined by X-ray
crystallography. Thermogravimetric analysis (TGA) was applied to complexes (3a–d). The
palladium complexes have been employed as catalyst for Suzuki-Miyaura cross coupling. The
N-aryl substituted complex 3b was a highly efficient precatalyst and successfully employed in
Suzuki-Miyaura cross coupling reactions of (hetero)aryl chlorides with arylboronic acids in air.
In addition, the oxidative addition step of the reaction mechanism involving chlorobenzene and
Available online
Keywords:
Piperidoimidazolin-2-ylidene
Palladium
Suzuki-miyaura coupling
PEPPSI-Pd-NHC
DFT calculations
the catalysts 3a, 3b, 3c and 3d were computationally investigated by the DFT-ω-B97X-D
method and complete agreement were obtained with the catalytic results. To measure σ-donating
and π-acceptor properties of the new ligands, the rhodium carbonyl complexes were also
prepared.
2
009 Elsevier Ltd. All rights reserved.
1
. Introduction
N-heterocyclic carbenes (NHCs) have attracted great interest
in various fields of chemistry since the discovery of the first
1
stable NHCs in the late 1980s and early 1990s. Among them,
five-membered
heterocycles
imidazol-2-ylidene
and
imidazolin-2-ylidene (A) and ring expanded analogue
tetrahydropyrimidin-2-ylidene (B) are now known as normal
2
NHCs (Figure 1). By varying the number and the location of
the heteroatoms in the core structure of the NHCs,
unsymmetrical NHCs (uNHCs) can be generated. The variation
of the substituents bound to the backbone can also lead to
uNHCs. Many structural modifications, including steric tuning
and changing the ligand backbone structure, had been pursued
Figure 1.
Organ and co-workers reported pyridine stabilized NHC
palladium complexes (PEPPSI-Pd) showing high activity
towards C-C and C-N cross-coupling reactions. Extensive
studies on the structure and activities of PEPPSI-Pd complexes
have been published since 2006.
NHC moiety and replacement of 3-chloropyridine by other
ligands have attracted great interest in order to obtain better
catalytic performance.
7
3
on uNHC ligands. More recent studies have shown that the
annulations of the 1,5- or 3,4-position of the imidazole ring also
influence the electronic and steric properties of the resulting
8-10
Both modification of the
4,5
complexes. Due to their steric demand and the synergy of
inductive and mesomeric effects of the heteroatoms in vicinity
to the carbenic center, their stability and donating ability is
11
6
excellent as an uNHCs ligands. For this purpose, herein, we
Imidazol-2-ylidene,
4,5-dihydro-imidazol-2-ylidene
or
compared NHC ligand (type C) with the analogues (A and B)
and also investigated the influence of N-substituents on the
catalytic activity of the system.
benzimidazol-2-ylidene based NHC systems were used in
almost all these studies. In a recent study, Cavell et al. have
published ring expanded PEPPSI-Pd complexes and their
catalytic activity on cross coupling transformations. They used
aryl halides for Suzuki-Miyaura reaction and obtained good
yields.
12

2
Tetrahedron
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In this work, a series of facile-prepared PEPPSI-Pd-uNHC
Thermogravimetric analysis (TGA) was applied to
complexes
complexes and their catalytic application in Suzuki-Miyaura
cross-coupling aryl chlorides with aryl boronic acid derivatives
is reported. Moreover, the present study includes detailed
investigations of the sterically hindered N-Aryl substituted
piperidoimidazolin-2-ylidene PEPPSI-Pd complex 3b in terms
of catalytic activity on a broad variety of substrates, catalytic
conditions (solvent, base, temperature). In comparison with the
3
a-d. TGA measurements of the complexes showed a
significant weight loss, occurring in different steps in the range
80-450 °C (see ESI). This is attributed to decomposition of
1
pyridine and piperidoimidazolin-2-ylidene. Metallic Pd or Pd
salts (PdBr, PdBr ) remained thermally intact under an inert gas
2
8h,i,12
atmosphere. The thermal decompositions of N-Aryl substituted
complexes (3a,b) occur in one step whereas N- benzyl
substituted complexes (3c,d) occur in multiple steps. The
lower thermal stability of 3c, d may be attributed to the benzyl
substitution on NHC ligand. The thermal stability of the
complexes played an important role on catalytic activity.
previously reported studies,
the complex 3b (0.01 mol %)
gave better yield using aryl chloride in a short time.
2
. Results and Discussion
2
.1. Synthesis and characterization of Pd(II) and Rh(I)
Complexes
8
In recent studies of PEPPSI-Pd-NHC complexes, the
Our synthetic strategy was based on the construction of the authors report that the catalytic properties of this type
annulated N-heterocyclic carbene core from readily available
building blocks, 2-aminomethyl-piperidine and 2-
complexes in cross-coupling reactions can changeable with
both the large σ- donating of NHC ligands and steric hindrance
imported by the bulky N-aryl substituents employed systems.
piperidinemethanol (Figure 2). The benzyl substituted
piperidoimidazolinium salts were prepared according to our
4a
1
13
previous studies. In the H and C spectra of N-aryl or benzyl
substituted piperidoimidazolinium salts (2a-d), the
characteristic peaks due to N-CH-N protons and carbons were
observed at 8.41 (2a), 8.42 (2b) and 8.55 (2d) ppm and at 156.5
1
13
(
2a), 156.4 (2b) and 159.5 (2d) ppm in the H and C NMR
spectra, respectively.
Figure 3. The synthesis of the palladium complexes 3a-d.
With this in mind, the rhodium complexes (4a-c) were
prepared by reaction of the rhodium dimer [Rh(µ-
OMe)(COD)]2
with
two
equivalents
of
the
piperidoimidazolinium salts 2a-c (Figure 4). They were
purified by chromatography on silica gel. These complexes
were observed to be stable towards air and moisture. They
13
exhibit characteristic C chemical shift, which provide a useful
diagnostic tool for metal carbene complexes. The most
13
significant resonance in the C NMR spectra of 4a-c is
assigned to the metal carbene carbon at 209.1 (4a), 209.5 (4b)
103
13
and 211.2 (4c) ppm. Coupling constant J ( Rh- C) for the
new complexes (4a-c) are comparable to those found for
rhodium-NHC complexes that have been described
Figure 2. The synthesis of the piperidoimidazolinium salts 2a-d.
4a,15
previously.
Because the nature of substitution pattern of the employed
NHC ligand has great influence on the catalytic activity,
PEPPSI-Pd complexes (3a-d) with different
1
3
piperidoimidazolin-2-ylidene were prepared in pyridine.
However, Organ showed that an (NHC)PdCl (pyridine)
2
complex is more active than the (NHC)PdCl (3-chloropyridine)
2
complex, suggesting that this improved activity could be due
either to a higher dissociation rate of the pyridine or to a higher
14
tendency to recoordinate to the species in solution. The
reaction of the ligand precursors with excess NaBr and
Pd(OAc) in neat pyridine under argon atmosphere affords (3a-
Figure 4. The synthesis of the rhodium complexes.
2
d) in 45 to 80 % yields (Figure 3). The Pd(II) complexes are air
and moisture stable yellow solids. The complexes (3a-d) were
characterized by NMR spectroscopy and exhibit good solubility
The v(CO) measurement of [MCl(NHC)(CO) ], (M = Rh, Ir)
2
is the most commonly used method to determine electron donor
13
15,16
in CH Cl , CHCl and DMSO. The C NMR spectra display
2
2
3
ability of NHCs.
The [Ni(NHC)(CO) ] complexes are also
3
the resonance due to the carbene carbon atoms at δ = 179.1,
76.8, 178.4, 179.4 ppm for the complexes 3a-d respectively.
The benzylic protons in N-benzylic piperidoimidazolin-2-
ylidene Pd complexes (3c, 3d) display a singlet corresponding COD complexes (4a, 4c) were converted straight forwardly to
to a total of two protons at 5.29 (3c) and 5.30 (3d) ppm.
used but rhodium or iridium preferred because of the toxicity of
1
[Ni(CO) ] used as starting material in this case. To determine σ-
3
donating ability of piperidoimidazolin-2-ylidene ligand, the
the corresponding carbonyl derivatives 5a and 5c, which

3
ACCEPTED MANUSCRIPT
allowed the electronic nature of the aryl or benzyl substituted
piperidoimidazolin-2-ylidene ligand to be inferred from the IR
spectra. The N-aryl substituted carbene complex 5a exhibited
(S) and C3B (R) in 3c. Four C-H…Br and a C-H..N type
intramolecular interactions are present in the crystal structure of
3a (Figures S2 and Table S2, ESI). The molecular packing of
the complexes are stabilized by a combination of two C−H…Br
and two C-H…π type intermolecular interactions for 3a and
two C−H…Br, a C-H…π and a π…π type intermolecular
interactions for 3c (Figures S3-6 and Table S3, ESI). For both
structures, these interactions those Br atoms involved may
cause a departure from the ideal value of 180° for trans angles
of Br-Pd-Br.
-
1
lower wave numbers (5a: 2071.0 and 1992 cm-1, ν (CO) cm =
av
-1
-
1
2
032; 5c: 2072 and 1993 cm , ν (CO) cm = 2033).
av
Additionally, the complex 5c´ did not give rise to difference
when it was compared to 5c (Figure 5).
2
Figure 5. The carbonyl stretching frequencies of [Rh(NHC)X(CO) ]
Figure 6. The molecular structures of 3a and 3c with displacement
ellipsoids drawn at the 30% probability level. Only molecule A of 3a and
the major components of the disordered atoms of 3c are shown for clarity.
Selected bond lengths (Å) and angles (°):Complex 3a; Pd1-C1 1.949(7),
Pd1-N1 2.089(6), Pd1-Br2 2.4301(11), Pd1-Br1 2.4506(10), C1-Pd1-N1
177.9(3), Br2-Pd1-Br1 171.78(4), Complex 3c; Pd1-C1 1.962(7), Pd1-N1
2.095(6), Pd1-Br2 2.4178(15), Pd1-Br1 2.4112(16), C1-Pd1-N1 176.5(3),
Br2-Pd1-Br1 176.23(7).
complexes (X: Cl, Br).
This observation is in accordance with earlier report by
16
Hahn. The aryl substituted piperidoimidazolin-2-ylidene (5a)
was found to be relatively better electron donor than benzyl-
analogues (5c, 5c´). Moreover, it is seen obviously that the
values of carbonyl frequencies of the complexes (5a, 5c, 5c´)
fall into between the types of NHC A and B. This observation
indicates that the electronic and steric influences of the N-
substituents are contributed to some extent on the electron
donating property of the NHC ligand.
2.3. Catalytic Suzuki-Miyaura Coupling Reaction with Pd(II)
Complexes
We investigated the activity of complexes 3a-d as catalysts
for the coupling of 4-chloroacetophenone with phenylboronic
acid under air and argon atmosphere (Figure 7). The complex
2
.2. Structural Studies
The molecular structures of complexes 3a and 3c were
3
b was found to be the most active catalyst among all of these
complexes tested. The sequence of the activity is 3b > 3a >
c > 3d. The aryl-substituted complexes (3a, 3b) were more
determined by single crystal X-ray diffraction analysis. Details
of data collection and refinement are presented as Supporting
Information (Table S1, ESI). The structural analysis display the
presence of slightly distorted square-planar coordination
environments defined by the coordination of the metal to the
pyridine ligand, the NHC ligand and the bromine atoms in a
trans arrangement as shown in Figure 6. In 3a, the asymmetric
unit contains two symmetry independent molecules, denoted A
and B, which do not differ significantly except disordered NHC
ring appeared in molecule B (Figure S1, ESI). The palladium-
NHC bond lengths in 3a and 3c are in agreement with the
values found in our previously characterized Pd-NHC
3
efficient than their benzyl analogues (3c, 3d). To confirm the
decomposition of complexes (3a, 3c) to Pd nanoparticles, the
complexes (3a, 3c) were investigated (initial, with the addition
0
of KOH and at 65 C) in CDCl . A direct comparison between
3
1
catalysts 3a and 3c was performed by H NMR analysis, which
revealed different catalytic behavior for two complexes (see
ESI). The catalyst 3a also proved to be competent in this
transformation, giving yields comparable those for the catalyst
3
c. A shorter induction period was present for 3a relative to 3c,
0
which may be related to the reduction to the active Pd species.
The performance of the catalytic activity of the complexes
revealed that improvement in activity could be reached not only
by using the rigid architecture of the NHC ligand, but also by
changing the substituents on the nitrogen atoms in NHC
ligands.
10a,b,17
complexes.
The NHC ring of 3a adopts an envelope
conformation in molecule A and also in the minor component
of molecule B, and a twisted conformation in the minor
component of molecule B. In 3c, the conformation of
disordered NHC ring is envelope and twisted for the major and
minor components, respectively. In molecule A of 3a, NHC
ring is rotated with respect to the coordination plane by 88.3(4).
In molecule B of 3a, NHC ring with major and minor
components are oriented at dihedral angles of 68.7(5)° and
The catalytic activities have impressed by both the rigid
architecture of the NHC ligand and the substituents on the
nitrogen atoms in NHC ligands. Moreover, the thermal stability
7
7.5(6)°, respectively, with the coordination plane, whereas of the complexes played an important role on catalytic activity.
corresponding angles are 73.8(6)° and 78.8(6)° in 3c. Following
Because of the higher thermal stability and lower energy
atoms in NHC rings are chiral centers with the absolute barriers, 3a and 3b exhibit higher catalytic activity. The above
configurations: C3 (S), C24A (S) and C24B (R) in 3a, and C3A
experimental results stabilities of 3c to comparison 3a, which

4
Tetrahedron
ACCEPTED MANUSCRIPT
within 2 min.
prompted us to investigate the mechanism by the density
functional theory (DFT) method.
Formation of active catalyst
N
N
Br
N
N
(
CH
3
)
2
CHOH, KOH
CO
Pd(0)
Pd(II)
N
-Py, -2KBr, -(CH )
3 2
Br
2 n
(CH )
(
CH
2
)
n
3a'-d'
3
a-d
Ar
Ar
Oxidative Addition (Rate Determining) Step
#
Cl
C
Cl
N
N
∆G
activation
free energy)
N
N
(
Pd(II)
Pd(0)
(
a)
(CH2)n
2 n
(CH )
Ar
Ar
TS_3a'-d'
Reactant complex
N
N
Cl
Ar = a: -C
b: -C
c: -CH C H (CH ) -2,4,6; n = 1
6 2
H (CH
3
3
) -2,4,6;n = 0
Pd(II)
6
H
3
3 2 2
[CH(CH ) ]
-2,6;n = 0
2
6
2
3 3
d: -CH C H [CH(CH ) ] -2,4,6;n = 1
2
6
2
3
2 3
(CH2)n
Ar
Product
Figure 8. Representative initial steps of the mechanism of Suzuki-Miyaura
coupling reaction with Pd(II) complexes (3a-d).
(
b)
Figure 7. Time dependency of catalytic Suzuki-Miyaura coupling
reaction by complexes 3a-d under in air (a) and argon atmosphere (b).
The mechanism of Suzuki-Miyaura coupling reaction with
Pd(II) complexes includes oxidative addition, transmetallation
Figure 8 depicts the representative initial steps of the
Suzuki-Miyaura coupling reaction mechanism, the oxidative
addition paths of the 3a′, 3b′, 3c′ and 3d′ active catalysts with
chlorobenzene while the corresponding activation Gibbs free
energy barrier values of these paths obtained with ω-B97X-D
method, % probability based on Boltzmann distribution
18,19
steps and reductive elimination.
The first step (the oxidation
step) of this coupling reaction is generally the slowest step that
determined the reaction rate. Recently, it is shown that the formula, the calculated and experimental percent initial
[
Pd(NHC)(R-allyl)Cl] type catalysts are rather active in the
conversion rates are given in the Table 2. The ω-B97X-D
barrier height order is 3b < 3a < 3c < 3d, leading to the
20
Suzuki−Miyaura coupling reaction and their activity comes
from monoligated [NHC-Pd ] complexes which serves as active theoretical activity sequence of 3b > 3a > 3c > 3d. The
0
21
catalytic species. In the light of these information, we
proposed mechanism for the oxidative addition step
accepting as the rate determining step) involving the
difference in activation free energy barriers let us calculate
%probability of molecules passing through these barriers. %
initial conversion rate, which can be defined as number of
molecules passing through activation barrier under exactly the
same conditions out of 100 molecules, is calculated using %
probabilities. The last column gives experimental conversion
percent under air atmosphere within 2 min. As seen from the
table, theoretical and experimental initial conversion rates well
agree with each other.
a
(
0
monoligated [NHC-Pd ] complex (Figure 8). Specifically, we
computationally determined the activation energy barriers of
oxidative addition step involving benzene chloride and active
catalysts, 3a’, 3b’, 3c’ and 3d’, with DFT-ω-B97X-D method
that gives better accuracy than the commonly used DFT-
B3LYP due to inclusion of dispersion interactions.
Table 2. Activation free energy barriers of oxidative addition paths of the
Figure 9 displays the important geometrical parameters of all
species involved the oxidative addition paths of the 3a′, 3b′, 3c′
and 3d′ active catalysts. As seen from the figure, chlorobenzene
approaches to active catalyst from its C atom attached to the Cl
atom, hence each oxidative addition step starts with an active-
3
a′, 3b′, 3c′ and 3d′ active catalysts with benzene chloride.
#
#
%Initial
%Parob Conversio
n rate
%Initial
Conversio
n rate
Active
ꢀG
ꢀꢀ G
catalyst (kcal/mol (kcal/mol
s
)
)
b
(theo)
(exp)
3
3
3
3
b’
a’
c’
11.26
11.96
12.86
13.31
0.00
0.71
1.61
2.06
100.00
34.90
9.13
67.24
23.47
6.14
48.72
28.21
15.38
7.69
catalyst-chlorobenzene
complex
(reac_3a’,
reac_3b’,
reac_3c’, reac_3d’). Then, both the C and Cl atoms continue to
approach Pd atom of the active catalyst (see TS structures),
finally the C and Cl atoms completely separate from each other
producing the oxidized active catalyst-chlorobenzene complex.
d’
4.68
3.15
a
#
b
Prob = 100 exp(-∆∆G /RT) at 298 K. Conversion percent under air atmosphere

5
ACCEPTED MANUSCRIPT
Figure 9. Important geometrical parameters of species in the oxidative addition path (the distances given are in Å units)
The conditions employed for the catalytic experiments are
After optimizing the reaction conditions, the palladium
depicted on Table 3. In order to improve the reactivity of our complex (3b) was also tested for various substrates in Suzuki-
catalytic system, we examined the influence of the base. We Miyaura reaction (Table 4). Generally, moderate to good
t
used Cs CO , KOH, K PO , NaOH and KO Bu (entries 1-5).
conversions 70-93% were obtained (Table 3). For arylboronic
acids with electron-withdrawing or electron donating groups,
such as fluorine, methyl, methoxy and formyl groups, the
reactions could afford the corresponding biaryls in moderate to
good yields. Apart from the electronic features, the impact of
steric hindrance aryl chlorides with 2,6-dimethylphenylboronic
2
3
3
4
The highest yield of the desired product was obtained with
KOH as the base (entry 1). Preferred solvent for Suzuki-
Miyaura cross-coupling reactions was i-PrOH as MeOH and
EtOH solvents lowered the catalytic activity. The decrease of
o
the reaction temperature from 82 to 25 C led to decrease the
yield (entries 8, 9). If the loading catalyst 3b was further acid was also investigated (Table 4, entries 11-13). para-
reduced to 0.01 to 0.001 mol%, the cross-coupling product was substituted chloride was compared with ortho-substituted ones,
obtained in satisfying yields of 95 and 70 % (entries 1, 10).
the former gave the 85% yield (Table 4, entry 11). When the
aryl chloride had multiple substituents, the reaction yield
exceeded 75% (Table 4, entries 1, 13) over 2 minutes.
Table 3. Different reaction conditions for Suzuki-Miyaura
Coupling with complex 3b for 2 min.
o
Entry
Solvent
Base
Loading
b(mol%)
T [ C]
Yield[%]
Cavell group’s synthesized various Pd-PEPPSI complexes
o
3
and obtained 96% yield at 80 C within 1 h for coupling
1
2
reaction of phenyl chloride with the phenylboronic acid. Lee
and co-workers performed the Suzuki-Miyaura reaction using
1
2
3
4
5
6
7
8
9
i-PrOH
i-PrOH
i-PrOH
i-PrOH
i-PrOH
EtOH
KOH
0.01
0.01
0.01
0.01
0.01
0.01
0.01
0.01
0.01
0.001
0.0001
82
82
82
82
82
78
65
50
25
82
82
95
70
53
33
31
54
22
35
12
70
28
K
3
PO
Cs CO
NaOH
4
o
8i
aryl bromides at 80 C and the yield’s up to 100 after 2 h. The
Pd-PEPPSI complexes were synthesized by Organ’s group
2
3
o
8b
showed 95% yield at 65 C within 24 h using aryl chlorides.
In comparison with these studies, our results are acceptable.
tBuOK
KOH
KOH
KOH
KOH
KOH
KOH
MeOH
i-PrOH
i-PrOH
i-PrOH
i-PrOH
1
1
0
1

6
Tetrahedron
ACCEPTED MANUSCRIPT
Table 4. The Suzuki-Miyaura reaction of aryl chlorides with phenylboronic
acids using catalyst
Table 5. The Suzuki-Miyaura reaction of heteroaryl chlorides with
arylboronic acids using catalyst 3b.
Entry
Ar
R
Yield
%)
(
1
2
3
4
5
6
7
8
9
2,5-Me-Ph
4-CN-Ph
4-CHO-Ph
2-Me-Ph
4-Me-Ph
4-MeO-Ph
Ph
H
75
89
93
77
70
71
80
82
77
74
85
73
71
77
74
73
72
71
75
72
85
H
H
H
H
H
H
4-CN-Ph
Ph
4-MeO
4-MeO
4-MeO
2,6-Me
2,6-Me
2,6-Me
4-F
1
1
1
1
1
1
1
1
1
1
2
2
0
1
2
3
4
5
6
7
8
9
0
1
4-Me-Ph
4-Me-Ph
2-Me-Ph
2,4-Me-Ph
4-Me-Ph
2-Me-Ph
4-Me-Ph
4-MeO-Ph
4-CN-Ph
2-Me-Ph
Ph
Reaction conditions: heteroaryl halide (1.0 mmol), arylboronic acid (1.2
mmol), KOH (2.0 mmol), catalyst 3b (0.01 mol %), IPA (1 mL), 10 min, in
air.
Double coupling of 1,4-dichlorobenzene and 2,6-
dichloropyridine with arylboronic acid derivatives was also
performed efficiently to give dicoupling products (Table 6).
The efficiency and selectivity towards diarylated product were
4-F
4-CHO
4-CHO
4-CHO
4-CHO
4-CHO
4-CHO
obtained in higher times.
Phenylboronic acid
,
4-
Formylphenylboronic acid, 2,6-dimethylphenylboronic acid, 4-
fluorophenylboronic acid were all successfully treated with 1,4-
dichlorobenzene to provide products in high yields (78-97%).
Encouraged by the very good results obtained with the catalyst
3
b for 1,4-dichlorobenzene, we decided to focus our research
on a more difficult substrate 2,6- dichloropyridine. As
expected, the double couplings of benzeneboronic acid, 4-
fluorophenylboronic acid with 2,6- dichloropyridine afforded
corresponding heteropolyarenes. An increase of the reaction
time to 1 h resulted in increase of the yield to 62 %.
2
4-NO -Ph
Reaction conditions: aryl halide (1.0 mmol), arylboronic acid (1.2 mmol),
KOH (2.0 mmol), catalyst (0.01 mol %), IPA (1 mL).
The new complexes have been demonstrated to be
significantly different from those of the related five- and six-
membered NHC-Pd-PEPPSI systems in cross-coupling
reactions. Overall, this procedure is suitable for this synthesis
of diverse biaryls through the cross-coupling reaction of
different aryl electrophiles and aryl boronic acids.
Table 6. The Suzuki-Miyaura reaction of 1,4-dichlorobenzene or 2,6-
dichloropyridine with arylboronic acids using catalyst 3b.
Heteroaryl chlorides (3-chloropyridine, 2-chlorothiophene,
3
-chlorothiophene) were also tested under our optimized
conditions using different aryl boronic acids (benzeneboronic
acid, 4-formylphenylboronic acid, 2,6-dimethylphenylboronic
acid, 4- fluorophenylboronic acid) and were produced in 63-
7
7% yield, demonstrating the applicability of heterocyclic
substrates in this procedure (Table 5). Initially, 3-
chloropyridine was explored. Reacting 4-formylphenylboronic
acid with 3-chloropyridine formed 74% of the expected
product. The arylboronic acids in combination with 2-
chlorothiophene gave the cross-coupling products in very good
yields. Having chloride at the 3-position of thiophene ring, the
decreasing the yields of the products was observed compared to
its 2-position analogue.
Reaction conditions for double coupling: aryl halide (1.0 mmol),
arylboronic acid (2.4 mmol), KOH (4.0 mmol), catalyst 3b (0.01 mol %),
IPA (1 mL), in air.
3
. Conclusions
New ligands and eleven metal complexes related with our
previously reported piperidoimidazolin-2-ylidene system were

7
ACCEPTED MANUSCRIPT
prepared and fully characterized. The molecular structures of
the complexes 3a and 3c were determined by X-ray
crystallography. The catalytic activities of the palladium
complexes (3a-d) were investigated in the Suzuki-Miyaura
coupling between aryl chlorides and arylboronic acids. In this
transformation, aryl-substituted pre-catalysts significantly
surpassed benzyl substituted pre-catalysts in efficiency. Pre-
catalyst 3d with a 2,4,6-tri(isopropyl)benzyl arm showed lower
activity; however the catalytic activity of 2,6-di(isopropyl)
substituted pre-catalyst (3b) was higher than that of 2,4,6-
mesityl substituted (3a). Moreover, the DFT calculations
revealed that catalysts 3a and 3b exhibit higher catalytic
activity than catalysts 3c and 3d due to having lower energy
barriers.
which was washed with diethylether until no colored impurities
remained. The resulting white powder was washed with water
(3x50.0 mL), and with technical grade diethyl ether (3x30.0
mL), dissolved in CH Cl , and the solution was dried with
2
2
sodium sulfate. After filtration, the concentrated solution was
layered with hexane, and the triflate salt 2a-b was isolated as
o
colorless crystals upon cooling at -10 C overnight.
o
1
2
a: Yield: 60%; m.p = 210-212 C. H NMR (CDCl , δ,
3
ppm): 8.35 (s, 1 H, NCH), 6.91 (s, 2 H, NC H (CH ) ), 4.43-
6
2
3 3
4
3
1
.46 (m, 1 H, piperidine-H), 4.26-4.32 (m, 2 H, piperidine-H),
.41-3.47(m, 1 H, NCH CH), 3.62-3.66 (m, 1 H, NCH CH),
2
2
.62-2.15 (m, 6 H, piperidine-H), 2.28, 2.24 (s, 9 H,
13
NC H (CH ) ). C NMR (CDCl , δ, ppm): 156.4 (NCH),
6
2
3 3
3
1
40.4, 135.6, 130.6, 130.1 (Ar-C), 120.1 (CF SO ), 60.2
3 3
(
1
NCH CH), 56.8, 46.4, 32.5, 25.9, 22.3 (piperidine-C), 21.2,
7.7 (NC H (CH ) ). Anal.Calc. for C H F N O S: C, 52.03;
6 2 3 3 17 23 3 2 3
4
. Experimental Section
2
The glass equipment was heated under vacuum in order to
H, 5.91; N, 7.14. Found: C, 52.15; H, 6.03; N, 7.33.
remove oxygen and moisture and then they were filled with
argon. The solvents were analytical grade and distilled under
argon atmosphere from sodium (toluene, diethyl ether, hexane,
o
1
2
b: Yield: 62%; m.p = 170-172 C. H NMR (CDCl , δ,
3
ppm): 8.44 (s, 1 H, NCH), 7.43 (t, J = 4.0 Hz, 1 H,
NC H [CH(CH ) ] ), 7.21 (d, 4.0 Hz, H,
NC H [CH(CH ) ] ), 4.37-4.49 (m, 1 H, piperidine-H), 4.27-
J
=
2
6
3
3 2 2
3 2 2
tetrahydrofuran),
P2O5
(dichloromethane).
Toluene,
6
3
tetrahydrofuran, dichloromethane, ethanol, hexane, pentane,
diethyl ether, acetonitrile, and methanol were obtained from J.
T. Baker and Merck. All reagents were purchased from
commercial sources and used as received. Ethyl N-2,6-di-iso-
4
2
.33 (m, 2 H, piperidine-H), 3.64-3.70 (m, 2 H, NCH CH),
2
.82-2.88 (m, 2 H, NC H [CH(CH ) ] ), 1.67-2.22 (m, 6 H,
6
3
3 2 2
i
13
piperidine-H), 1.37, 1.41 (d, J = 4.0 Hz, 12 H, Pr-H). C NMR
(CDCl , δ, ppm): 156.4 (NCH), 147.1, 146.6, 131.3, 129.9 (Ar-
C), 125.1 (CF SO ), 60.2 (NCH CH), 55.2, 46.6, 32.8, 28.8,
2
2
3
propyl-phenylformamidinate, ethyl N-mesityl-formamidinate
2
3
1
13
3
3
2
and 2c
were prepared according to literature. H and
C
2
6.2 (piperidine-C), 18.7 (NC H [CH(CH ) ] ). Anal. Calc. for
6 3 3 2 2
NMR spectra were taken with Varian AS 400 Mercury
1
3
C H F N O S: C, 55.28; H, 6.73; N, 6.45. Found: C, 55.21; H,
20 29 3 2 3
instrument operating at 400 MHz (1H), 100.56 ( C). CDCl
3
6
.63; N, 6.88.
d: Different benzylbromides (15.0 mmol) and
piperidoimidazole (1.86 g, 15.0 mmol) were refluxed in toluene
15.0 mL) for 4 h. The volume of the solution was reduced to
.0 mL, and diethyl ether was added to the remaining solution,
which was vigorously stirred and then decantated. The solid
residue was washed with diethyl ether (3 × 20.0 mL) to obtain
an orange solid, which was recrystallized from
methanol/diethyl ether (3 mL/20.0 mL). Yield: 52%; m.p= 209-
11 C. H NMR (DMSO, δ, ppm): 8.10 (s, 1 H, NCH), 7.07 (s,
H, NCH C H [CH(CH ) ] ), 2.78-3.32 (m, 5 H, piperidine-H,
was employed as solvent. Chemical shifts (δ) are given in ppm
relative to TMS; coupling constants (J) in Hz.
Thermogravimetric (TG) and differential thermogravimetric
2
(
DTG) curves were obtained using a Perkin–Elmer Pyris 6
(
5
0
analyzer in the range 50–950 C in alumina crucibles under
3
-1
0
nitrogen (flux rate: 20 cm min ) at a heating rate of 20 C min
-
1
using alumina as reference. The yields of catalytic
experiments were measured by GC Agilent brand (7890A
series) on a HP-5 capillary column and with a FID detector) in
Ege University in Faculty of Science at Department of
Chemistry.
o
1
2
2
2
6
2
3 2 3
NCH C H [CH(CH ) ] ), 1.35-1.73 (m, 6 H, piperidine-H),
2
6
2
3 2 3
4
.1. Synthesis of 1a-b
1
3
1
.12-1.19 (m, 18 H, NCH C H [CH(CH ) ] ). C NMR
2 6 3 3 2 3
A neat mixture of 2-piperidine methanol (3.2 g, 28.0 mmol) (DMSO, δ, ppm): 160.2 (NCH), 149.3, 148.2, 132.6, 130.1 (Ar-
and ethyl N-(2,6-diisopropylphenyl)formamidinate (6.37 g, C), 77.8 (NCH CH), 64.5 (NCH CH), 60.9,
8.0 mmol) was stirred at 160 °C for 3 h in a flask equipped (NCH C H [CH(CH ) ] ), 55.2, 46.6, 32.8, 28.8, 26.2
with a Dean-Stark condenser to remove ethanol. The residue (piperidine-C), 18.7 (NC H [CH(CH ) ] ). Anal. Calc. for
2
2
2
2
6
3
3 2 3
6
2
3 2 3
was dried under high vacuum, and the resulting orange oil (1a)
was used without further purification. By using the same
procedure as above, but with ethyl N-mesityl-formimidate (2.8
g, 28.0 mmol) and 2-piperidinemethanol (3.2 g, 28.0 mmol)
was obtained as a orange oil (1b). But the compounds were not
isolated exactly.
C H BrN : C, 65.55; H, 8.85; N, 6.65. Found: C, 66.74; H,
8.88; N, 6.80.
23 37 2
4
.3. General procedure of [PdBr (NHC)Py] complexes
2
The Pd(OAc) (65.0 mg, 0.3 mmol) was added to 2a (125.0
2
mg, 0.3 mmol) and NaBr (60.0 mg, 0.6 mmol) which was
dissolved in pyridine (5.0 mL) under argon atmosphere. The
reaction mixture was stirred 1 h at RT and then refluxed for 48
h. Meanwhile the reaction progress was controlled with layer
chromatography. After removal of the solvent under vacuum,
the precipitate was purified by column chromatography on
silica gel using CH Cl to give a yellow solid. The residue was
4
.2. Synthesis of aryl substituted piperidoimidazol-2-ylidene
derivatives salts, 2a-b
Amidine 1a-b (42.5 mmol) was dissolved in 20 mL of dried
o
CH Cl and cooled to -78 C. Diisopropylethylamine (8.9 mL,
2
2
5
1.0 mmol) was added to the solution, followed by the
2
2
dropwise addition of trifluoromethanesulfonicanhydride (7.1
mL, 42.5 mmol). The solution was stirred for 30 min at -78 C
and then warmed to room temperature. The volatiles were
removed under reduced pressure to afford an orange solid,
recrystallized from CH Cl / (C H ) O (v/v = 3:10 mL)
2 2 2 5 2
o
o
1
3
a: Yield: 45%; m.p = 296-298 C. H NMR (CDCl , δ,
3
ppm): 8.69-8.71 (m, 2 H, Py-H), 7.58-7.62 (m, 1 H, Py-H),
.14-7.18 (m, 2 H, Py-H), 6.95 (s, 2 H, NC H (CH ) ), 5.32 (dd,
7
6
2
3 3

8
Tetrahedron
ACCEPTED MANUSCRIPT
o
1
J = 16 Hz, 1 H, piperidine-H), 3.91-3.96 (m, 2H, NCH CH),
4a: Yield: 57.7 mg, 45%; m.p = 190-192 C. H NMR
(CDCl , δ, ppm): 7.00, 6.87 (s, 2 H, NC H (CH ) ), 5.41-5.50
2
3
.35-3.48 (m, 2 H, piperidine-H), 2.31, 2.47, 2.50 (s, 9 H,
3
6
2
3 3
13
NC H (CH ) ), 1.18-2.00 (m, 6 H, piperidine-H). C NMR
(m, 1 H, piperidine-H), 4.79-4.93 (m, 2 H, piperidine-H), 3.73-
6
2
3 3
(
CDCl , δ, ppm): 179.1 (NCN), 152.6, 138.5, 137.7 (Py-C), 3.83 (m, 2 H, NCH CH, COD-CH), 3.56-3.61 (m, 1 H, COD-
3
2
1
4
34.6, 129.8, 129.7, 124.4 (Ar-C), 59.9 (NHCH CH), 57.6,
CH), 3.18-3.28 (m, 2 H, NCH CH, COD-CH), 3.11-3.16 (m, 1
2
2
9.1, 32.8, 25.9, 23.7 (piperidine-C), 21.3, 20.2 (NC H (CH ) ).
H, COD-CH), 2.52, 2.05 (d, J = 4.0 Hz, 6 H, NC H (CH ) ),
6
2
3 3
6
2
3 3
Anal. Calc. for C H Br N Pd: C, 42.92; H, 4.63; N, 7.15.
2.34-2.39 (m, 2 H, piperidine-H), 2.32 (s, 3 H, NC H (CH ) ),
2
1
27
2
3
6 2 3 3
Found: C, 42.88; H, 4.52; N, 7.30.
1.81-1.95 (m, 8 H, piperidine-H, COD-CH ), 1.39-1.65 (m, 8
2
13
o
1
H, piperidine-H, COD-CH
2
). C NMR (CDCl
, δ, ppm): 208.3
3
3
b: Yield: 50%; m.p = 328-330 C. H NMR (CDCl , δ,
1
3
(
d, J
= 57.7, Rh-Ccarbene), 138.2, 138.1, 137.6, 137.5, 136.1,
Rh-C
ppm): 8.73-8.75 (m, 2 H, Py-H), 7.59-7.64 (m, 1 H, Py-H), 7.39
t, J = 8.0 Hz, 2 H, Py-H), 7.30 (d, J = 12.5 Hz, 2 H,
NC H [CH(CH ) ] ), 7.16-7.19 (m, 1 H, NC H [CH(CH ) ] ),
1
35.1 (Ar-C), 97.2 (d, J = 9.2 Hz, COD-CH), 69.4 (d, J = 14.0
(
Hz, COD-CH), 59.6 (NCH CH), 57.4, 49.5, 34.3, 32.9, 30.8,
2
6
3
3 2 2
6
3
3 2 2
3
0.6, 29.7, 27.6, 27.1, 23.7 (piperidine-C, COD-CH ), 21.0 20.4
2
5
.47 (dd, J = 4.4, 12.8 Hz, 1 H, piperidine-H), 3.43-4.04 (m, 6
(
NC H (CH ) ). Anal.Calc. for C H BrN Rh: C, 54.05; H,
6 2 3 3 24 34 2
H, NCH CH, piperidine-H, NC H [CH(CH ) ] ), 1.59-2.09 (m,
2
6
3
3 2 2
6
.43; N, 5.25. Found: C, 54.12; H, 6.51; N, 5.34.
6
H, piperidine-H), 1.46, 1.16 (t, J = 12.0 Hz, 12 H,
13
o
1
NC H [CH(CH ) ] ). C NMR (CDCl , δ, ppm): 179.6 (NCN),
4b: Yield: 75.2 mg, 45%; m.p= 201-203 C. H NMR
(CDCl , δ, ppm): 7.29-7.34 (m, 2 H, NC H [CH(CH ) ] ), 7.11-
6
3
3 2 2
3
1
6
2
52.3, 148.3, 137.4 (PyC), 134.2, 129.4, 124.5, 124.2 (Ar-C),
0.1 (NCH CH), 59.5 (NC H [CH(CH ) ] ), 49.3, 32.3, 28.3,
3
6
3
3 2 2
7.14 (m, 2 H, NC H [CH(CH ) ] ), 5.43-5.54 (m, 1 H,
2
6
3
3 2 2
6
3
3 2 2
6.9,
26.8
(piperidine-C),
25.6,
24.4,
23.4
piperidine-H), 4.83-4.94 (m, 2 H, piperidine-H), 3.71-3.88 (m,
(
NC H [CH(CH ) ] ). Anal. Calc. for C H Br N Pd: C, 45.77; 3 H, NCH CH, COD-CH), 3.55-3.60 (m, 1 H, COD-CH), 3.33-
6
3
3 2 2
24 33
2
3
2
H, 5.28; N, 6.67. Found: C, 45.79; H, 5.53; N, 6.84.
3.45, 2.88-2.97 (m, 2 H, COD-CH), 2.69-2.80, 2.27-2.39 (m, 2
o
1
H, NC H [CH(CH ) ] ), 1.72-2.14, 1.62-1.55, 1.31-1.38 (m, 10
6 3 3 2 2
3
c: Yield: 80%; m.p= 272-274 C. H NMR (CDCl , δ,
3
H, piperidine-H, COD-CH ), 1.09, 1.20, 1.49 (m, 12 H,
2
ppm): 9.02-9.04 (m, 2H, Py-H), 7.12-7.76 (m, 1 H, Py-H),
.29-7.33 (m, 2 H, Py-H), 6.87 (s, 2 H, NCH C H (CH ) ), 5.25
s, 2 H, NCH C H (CH ) ), 5.08-5.12 (dd, J = 4.4, 13.2 Hz, 1
H, piperidine-H), 3.66-3.71 (m, 1 H, NCH CH), 3.26-3.35 (m,
H, NCH CH, piperidine-H), 2.73-2.77 (m, 1 H, piperidine-H),
13
NC H [CH(CH ) ] ). C NMR (CDC , δ, ppm): 208.9 (dd, J
6
3
3 2 2
l3
Rh-
7
(
2
6
2
3 3
=
46.0, Rh-Ccarbene), 149.3, 146.1, 135.9, 128.7, 124.9, 123.5
Ar-C), 97.6 (d, J = 6.0 Hz, COD-CH), 68.2 (dd, J = 14.0 Hz,
COD-CH), 60.4, 60.1, 59.5, 59.1, 50.0, 48.6, 34.6, 32.6, 30.3,
C
2 6 2 3 3
(
2
2
2
2
2
9.7, 28.1, 27.2, 26.6, 25.2, 23.1 ( NC H [CH(CH ) ] ).
6 3 3 2 2
.27, 2.41 (s, 9 H, NCH C H (CH ) ), 1.36-1.96 (m, 6 H,
2
6
2
3 3
1
3
Anal.Calc. for C27H40BrN Rh: C, 56.36; H, 7.01; N, 4.87.
2
piperidine-H). C NMR (CDCl , δ, ppm): 178.4 (NCN), 152.4,
38.4, 137.8 (PyC), 137.7, 129.2, 128.3, 124.5 (Ar-C), 59.2
NCH CH), 53.8 (NCH C H (CH ) ), 48.6, 48.3, 31.9, 25.5,
3.2 (piperidine-C), 20.8, 20.9 (NCH C H (CH ) ). Anal. Calc.
2 6 2 3 3
3
Found: C, 56.41; H, 7.19; N, 5.02.
1
(
2
o
1
4c: Yield: 447.2 mg, 68%; m.p= 168-170 C. H NMR
(CDCl , δ, ppm): 6.85 (s, 2 H, NCH C H (CH ) ), 5.25-5.48
2
2
6
2
3 3
3
2
6
2
3 3
for C H Br N Pd: C, 43.91; H, 4.86; N, 6.98. Found: C,
(m, 1 H, NCH C H (CH ) ), 4.87-5.12 (m, 3 H, COD-CH,
2
2
29
2
3
2 6 2 3 3
4
4.01; H, 4.81; N, 7.11.
NCH C H (CH ) , 3.45-3.56 (m, 4 H, COD-CH, piperidine-H),
2 6 2 3 3
o
1
3.09-3.21 (m, 2H, NCH
2
CH), 2.57-2.64 (m, 2 H, piperidine-H),
3
d: Yield: 68%; m.p = 322-324 C. H NMR (CDCl , δ,
3
2
.36, 2.26 (s, 9 H, NCH C H (CH ) ), 2.25-2.49 (m, 4 H,
2
6
2
3 3
ppm): 9.04 (dd, J = 5.6 Hz, 2 H, Py-H), 7.35 (t, J = 7.6 Hz, 1 H,
Py-H), 7.32 (t, J = 5.6 Hz, 2 H, Py-H), 7.03 (s, 2 H,
13
piperidine-H), 1.86-1.97, 1.29-1.50 (m, 8 H, COD-CH2).
C
NMR (CDC , δ, ppm): 208.9 (dd, J
= 46.0, Rh-Ccarbene),
l3
Rh-C
NCH C H [CH(CH ) ] ),
5.27-5.35
(m,
2
H,
2
6
2
3 2 3
1
9
38..2, 137.5, 129.2, 129.1 (CH C H (CH ), 98.5, 98.4, 98.1,
8.0 (COD-CH), 70.1, 69.5, 67.8, 67.4 (COD-CH), 59.1
2 6 2 3
NCH C H [CH(CH ) ] ), 5.07-5.10 (m, 1 H, piperidine-H),
.28-3.68-9 (m, 5 H, NCH CH, NCH C H [CH(CH ) ] ), 2.79-
2 2 6 2 3 2 3
.90 (m, 2 H, piperidine-H), 1.37-1.95 (m, 6 H, piperidin-H),
.23-1.27 (m, 18 H, NCH C H [CH(CH ) ] ). C NMR
CDCl , δ, ppm): 178.2 (NCN), 152.5, 149.1, 148.9 (PyC),
37.7, 125.5, 124.4, 121.3 (Ar-C), 59.3 (NCH CH), 53.9
2
NCH C H [CH(CH ) ] ), 48.4, 46.5,
2
6
2
3 2 3
3
2
1
(
1
(
NCH CH), 54.1 (NCH C H (CH ) ), 48.3, 33.1, 32.2, 31.9,
2 2 6 2 3 3
1
3
31.7, 29.5, 28.4, 26.6, 26.1 (piperidine-C, CODCH
), 22.6
2
2
6
2
3 2 3
(
C H (CH ) -o-CH ), 20.7 (C H (CH ) -p-CH ). Anal. Calc. for
6
2
3 3
3
6
2
3 3
3
3
C H BrN Rh: C, 54.86; H, 6.63; N, 5.12. Found: C, 54.93; H,
2
5
36
2
6
.59; N, 5.25.
(
(
34.2, 31.6, 29.2
2
6
2
3 2 3
o
1
piperidine-C),
25.5,
24.4,
24.3, 23.9, 23.2
4c´: Yield: 423.4 mg, 70 %; m.p = 160-162 C. H NMR
(
NCH C H [CH(CH ) ] ). Anal. Calc. for C H Br N Pd: C,
(CDCl , δ, ppm): 6.80 (s, 2 H, NCH C H (CH ) ), 5.29-5.42
3 2 6 2 3 3
2
6
2
3 2 3
28 41
2
3
4
9.03; H, 6.03; N, 6.13. Found: C, 49.19; H, 6.12; N, 5.99.
(m, 1 H, NCH C H (CH ) ), 4.80-5.08 (m, 3 H, COD-CH,
2 6 2 3 3
NCH C H (CH ) , piperidine-H), 3.39-3.54 (m, 4 H, COD-CH,
2
6
2
3 3
4
.4. General procedure of [RhBr(NHC)COD] complexes
piperidine-H), 3.05-3.18 (m, 2H, NCH CH), 2.51-2.61 (m, 2 H,
2
piperidine-H), 2.32, 2.21 (s, 9 H, NCH C H (CH ) ), 2.24-2.42
[
Rh(µ-OMe)COD] (54.0 mg, 0.12 mmol) was added to 2a
2
6
2
3 3
2
(
m, 4 H, piperidine-H), 1.76-1.95, 1.47-1.21 (m, 8 H, COD-
(
100.0 mg, 0.24 mmol) and NaBr (46.0 mg, 0.48 mmol) which
was dissolved in dry toluene (6.0 ml) under argon atmosphere.
The reaction mixture was stirred 1 h at 25 C and then refluxed
for 48 h. Meanwhile the reaction progress was controlled with
layer chromatography. After removal of the solvent under
vacuum, the rhodium compound was purified by column
chromatography on silica gel using CH Cl to give a yellow
13
CH2). C NMR (CDCl , δ, ppm): 211.0 (dd, J = 45.0, Rh-
3
Rh-C
o
Ccarbene), 138.1, 137.4, 129.1, 128.9 (Ar-C), 98.2, 97.8 (d, J =
.0 Hz, COD-CH), 70.0, 67.5, (d, J = 14.0 Hz, COD-CH), 58.1
NCH C H (CH ) ), 54.1 (NCH CH), 48.0, 47.8, 33.2, 32.2,
6
(
2
6
2
3 3
2
3
2
5
2.1, 31.9, 29.4, 28.5, 26.1, 23.3, (piperidine-C, COD-CH2),
0.7 20.8 (NCH C H (CH ) ). Anal.Calc. for C H ClN Rh: C,
2
6
2
3 3
25 36
2
2
2
9.70; H, 7.21; N, 5.57. Found: C, 59.87; H, 7.75; N, 5.49.
solid. The residue was recrystallized from CH Cl / (C H ) O
2
2
2
5 2
(v/v = 3:10 mL)
4
.5. General procedure of [RhX(NHC)(CO) ] complexes
2

9
ACCEPTED MANUSCRIPT
The complex (4a) (120.0 mg, 0.2 mmol) was dissolved in
of optimization. To be able to obtain better energy values,
single point energy calculations were performed with ω-B97X-
D employing the triple split valence basis set 6-311+G(d,p) was
CH Cl (6.0 mL) and carbon monoxide was passed through the
2
2
solution for 3 h. After the completion of the time, volatiles were
removed in vacuo and residue was washed with cold n-pentane
to give a yellow solid.
2
6,27
used for C, H, O, N, and Cl atoms, while LANL2TZ+ECP
was employed for the Pd center in isopropyl alcohol medium
through integral equation formalism polarized continuum
o
-1
5
a: Yield: 85.6 mg, 79%; m.p= 182 C; v (CO) cm :
28
av
1
model (IEFPCM). All calculations were performed utilizing
2
4
032.2. H NMR (CDCl , δ, ppm): 6.91 (s, 2 H, NC H (CH ) ),
29
3
6
2
3 3
Gaussian 09 quantum chemistry program suite.
.72 (d, J = 12 Hz, 1 H, piperidine-H), 3.89-3.99 (m, 2 H,
NCH CH, piperidine-H), 3.39-3.43 (m, 1 H, NCH CH), 3.18-
4.8. X-ray Crystallography
2
2
3
2
1
2
.27 (m, 1 H, piperidine-H), 2.17-2.34 (m, 2 H, piperidine-H),
.29 (s, 9 H, NC H (CH ) ), 1.89-2.00 (m, 2 H, piperidine-H),
Single crystal X-ray diffraction data for 3a and 3c were
collected on an Agilent Diffraction Xcalibur diffractometer with
an Eos CCD area detector using graphite-monochromated Mo
Kα radiation (λ=0.71073 Å) at room temperature. The data
collection, cell refinement, and data reduction were executed
6
2
3 3
1
3
57-1.64 (m, 2 H, piperidine-H). C NMR (CDCl , δ, ppm):
3
00.1 (d, JRh-C = 39.0 Hz, Rh-Ccarbene), 185.9 (d, J = 52.0 Hz,
CO), 182.8 (d, J = 60.0 Hz, CO), 138.4, 134.9, 129.9, 128.9
Ar-C), 60.3, 57.4, 48.6, 34.1, 32.8, 23.3 (piperidine-C), 21.1,
(
2
4
28
using the CrysAlisPro program. The absorption corrections
2.3 (NC H (CH ) ). Anal. Calc. for C H BrN O Rh: C,
6 2 3 3 18 24 2 2
29
were done analytically using a multifaceted crystal model.
4.74; H, 5.01; N, 5.80. Found: C, 44.82; H, 5.13; N, 5.88.
The crystal structures were solved by direct methods using
o
-1
3
0
5
c: Yield: 74.2 mg, 82%; m.p= 168-170 C; v (CO) cm :
av
SHELXS-97 and the refinement (on F2) was carried out by
1
30
2
033.0.
H
NMR (CDCl3, δ, ppm): 6.86 (s, 2 H,
full-matrix least square techniques using SHELXL-97. All
non-hydrogen atoms were refined anisotropically. All hydrogen
atoms were treated as riding atoms (C-H= 0.95 to 0.99 Å).
NCH C H (CH ) ), 5.05-5.11 (m, 1 H, NCH C H (CH ) ),
2
6
2
3 3
2
6
2
3 3
4
3
2
.55-4.71 (m, 2 H, piperidine-H, NCH C H (CH ) ), 3.67-3.71,
2 6 2 3 3
3
1
.13-3.41, 2.77-2.87 (m, 4 H, piperidine-H, NCH CH), 2.33,
2
Molecular3 graphics are prepared using ORTEP-3
and
2
.26 (s, 9 H, NCH C H (CH ) ), 2.24-2.41 (m, 2 H, piperidine- PLATON software. In both structures, some of the atoms of
2
6
2
3 3
1
3
H), 1.44-1.89 (m, 4 H, piperidine-H). C NMR (CDCl , δ,
ppm): 199.3 (d, JRh-C = 45.0 Hz, Rh-Ccarbene), 186.7 (d, J = 70.0
Hz, CO), 182.8 (d, J = 77.0, CO), 137.8, 129.4, 129.3, 128.3
3
the NHC rings (N5, C24, C25, C26, C27, C28 in 3a and N2,
C3, C4, C5, C6, C7 in 3c) were disordered over two different
orientations (letters A and B for minor and major components,
respectively). The refinements converged to final occupancies
of 0.521(6)/0.479(6) in 3a and 0.514(8)/0.486(8) in 3c. Equal
Uij constraints (EADP) were used for all of the disordered atom
pairs.
(Ar-C), 59.9, 59.4, 54.1, 48.8, 32.3, 25.5, 23.1 (piperidine-C,
NCH C H (CH ) ), 20.5, 20.9 (NCH C H (CH ) ). Anal.Calc.
for C H BrN O Rh: C, 45.89; H, 5.27; N, 5.63. Found: C,
4
2
6
2
3 3
2
6
2
3 3
1
9
26
2
2
5.93; H, 5.25; N, 5.68.
o
-1
5
c´: Yield: 59.7 mg, 74%; m.p= 162-164 C; v (CO) cm :
av
CCDC 1053359 (3a) and 1053360 (3c) contain the
supplementary crystallographic data for this paper. These data
can be obtained free of charge from The Cambridge
1
2
032.3.
H
NMR (CDCl3, δ, ppm): 6.84 (s, 2 H,
NCH C H (CH ) ), 5.02-5.09 (m, 1 H, NCH C H (CH ) ),
2
6
2
3 3
2
6
2
3 3
4
3
2
.53-4.69 (m, 2 H, piperidine-H, NCH C H (CH ) ), 3.64-3.75,
2 6 2 3 3
Crystallographic
Data
Centre
via
.12-3.42, 2.76-2.85 (m, 4 H, piperidine-H, NCH CH), 2.32, http://www.ccdc.cam.ac.uk/data request/cif.
.26 (s, 9 H, NCH C H (CH ) ), 2.24-2.37 (m, 2 H, piperidine-
H), 1.37-1.87 (m, 4 H, piperidine-H). C NMR (CDCl , δ,
ppm): 199.2 (dd, JRh-C = 40.0 Hz, Rh-Ccarbene), 186.3 (dd, J =
2
2
6
2
3 3
1
3
3
Acknowledgements
1
1
6.0 Hz, CO), 182.7 (d, J = 76.0, CO), 137.8, 129.4, 128.6,
28.3 (Ar-C), 59.9, 59.4, 54.1, 48.9, 32.4, 26.2, 23.1
All calculations reported in this paper were performed at
High Performance and Grid Computing Center (TRUBA
resources), ULAKBIM. The authors also acknowledge Dokuz
Eylül University for the use of the Agilent Xcalibur Eos
diffractometer (purchased under University Research Grant no.
(piperidine-C,
NCH C H (CH ) ),
20.5,
20.9
2
6
2
3 3
(NCH C H (CH ) ). Anal. Calc. for C H ClN O Rh: C, 50.40;
2
6
2
3 3
19 26
2
2
H, 5.79; N, 6.19. Found: C, 50,62; H, 5.63; N, 6.35.
.6. General procedure for the Suzuki coupling reaction
A two-necked 25.0 mL flask fitted with a reflux condenser acknowledged.
2
010.KB.FEN.13). Financial support from Ege University
4
(project 2010‐FEN ‐046 and 2010‐ Fen‐076) is gratefully
and septum was charged with aryl halide (1.0 mmol),
phenylboronic acid (1.2 mmol), KOH (2.0 mmol),
diethyleneglycol-di-n-butylether (0.6 mmol, internal standard),
and the palladium-pyridine catalyst (0.01 mol %) in isopropyl
alcohol (1.0 mL) was added. The mixture was heated to 82 C
under an air atmosphere. The conversion was monitored by gas
chromatography.
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