Synthesis of palladium complexes derived from imidazolidin-2-ylidene ligands and used for catalytic amination reactions

Article abstract of DOI:10.1002/aoc.3541

N-Aryl amination and the Buchwald–Hartwig reaction are of great synthetic and industrial interest and scientists accept their usefulness and versatility for obtaining arylamines. In this study Ag–N-heterocyclic carbene complexes were used as transmetallation reagents for the synthesis of Pd–N-heterocyclic carbene complexes. The new Pd–N-heterocyclic carbene complexes were characterized using elemental analysis and ¹H NMR, ¹³C NMR and infrared spectroscopies. The crystal structure of one, namely dichlorobis[1,3-bis(2-methylbenzyl)imidazolidin-2-yliden]palladium(II), is presented. The activity of the Pd(II) complexes in the coupling reaction of anilines or amines with bromobenzene was investigated. These complexes exhibited high catalytic activities in the direct synthesis of triarylamines and secondary amines in a single step. Copyright

Full text of DOI:10.1002/aoc.3541

Full paper
Received: 5 April 2016
Revised: 11 May 2016
Accepted: 20 May 2016
Published online in Wiley Online Library
(wileyonlinelibrary.com) DOI 10.1002/aoc.3541
Synthesis of palladium complexes derived from
imidazolidin-2-ylidene ligands and used for
catalytic amination reactions
a
a
b
c
Emine Özge Karaca , Nevin Gürbüz , Onur Şahin , Orhan Büyükgüngör
a
and İsmail Özdemir *
N-Aryl amination and the Buchwald–Hartwig reaction are of great synthetic and industrial interest and scientists accept their
usefulness and versatility for obtaining arylamines. In this study Ag–N-heterocyclic carbene complexes were used as trans-
metallation reagents for the synthesis of Pd–N-heterocyclic carbene complexes. The new Pd–N-heterocyclic carbene complexes
1
13
were characterized using elemental analysis and H NMR, C NMR and infrared spectroscopies. The crystal structure of one,
namely dichlorobis[1,3-bis(2-methylbenzyl)imidazolidin-2-yliden]palladium(II), is presented. The activity of the Pd(II) complexes
in the coupling reaction of anilines or amines with bromobenzene was investigated. These complexes exhibited high catalytic
activities in the direct synthesis of triarylamines and secondary amines in a single step. Copyright © 2016 John Wiley & Sons, Ltd.
Additional supporting information may be found in the online version of this article at the publisher’s web site.
Keywords: N-heterocyclic carbene; imidazolidin-2-ylidene; palladium; amination
reactions and oxidation reactions, and more recently a heteroge-
Introduction
neous palladium–N-heterocyclic carbene system has been ex-
[
16,17]
Heterocyclic compounds are of importance because of their
plored for hydrogenation reactions.
[
1]
abundance in numerous natural products such as vitamins and
Within this context we have recently reported implementation of
imidazolidin-2-ylidene and benzimidazolidin-2-ylidine complexes
in C–N cross-coupling and their catalytic activity for aryl amination
[2]
[3]
alkaloids as well as pharmaceuticals of biological activity and
[
4]
electroactive materials. C–N bonds of aromatic compounds
supply access to nitrogen-containing molecules of great interest
in synthetic, biological, medicinal and materials sciences and that
[
18,19]
using bromobenzene and various anilines or amines.
Consid-
ering the growing interest in catalytic activity of palladium
complexes to act as dominant and efficient catalysts in amination
reactions, in this article we report six new N-heterocyclic carbene
palladium complexes from transmetallation of related Ag–N-
heterocyclic carbene complexes. All synthesized compounds were
[
5,6]
makes it an important transformation.
The Buchwald–Hartwig
amination is a chemical reaction used in organic chemistry for the
synthesis of carbon–nitrogen bonds via palladium-catalysed
cross-coupling of amines with aryl halides. The numerous
applications of Pd–N-heterocyclic carbene systems have been
comprehensively reviewed.
N-heterocyclic carbenes have been used widely in organo-
1
13
characterized using H NMR, C NMR and infrared (IR) spectros-
copies and elemental analysis, the results of which support the
proposed structures. The molecular and crystal structure of the
dichlorobis[1,3-bis(2-methylbenzyl)imidazolidin-2-yliden]palla-
dium(II) (1a) complex was determined using the single-crystal X-ray
diffraction technique. In addition, we examined the activity of the
synthesized palladium complexes in the Buchwald–Hartwig
amination reaction.
[
7–13]
[
14]
metallic chemistry and coordination chemistry for 30 years.
Organometallic N-heterocyclic carbene-based complexes have
demonstrated their wide scope of application, and thus their
usefulness, in the synthesis of complex and valuable molecules.
For the preparation of reusable catalysts these important applica-
tions transform N-heterocyclic carbene ligands into suitable
candidates. The potential offered by N-heterocyclic carbenes as
supporting ligands in palladium-mediated catalysis is evident from
the continuously growing number of reactions mediated by such
*
Correspondence to: İsmail Özdemir, Inönü University, Catalysis Research and
[15]
Application Center, 44280, Malatya, Turkey. E-mail: iozdemir@inonu.edu.tr
complexes.
In spite of the certain utility of (hetero)bidentate
phosphine-based ligands (vide supra), with a detailed survey of
the literature it can be seen that the application of conceptually
related heterobidentate N-heterocyclic carbenes has received
relatively little attention in Buchwald–Hartwig amination chemistry.
Palladium–N-heterocyclic carbene systems have been successfully
employed in various reactions such as C–C and C–N coupling
a Inönü University, Catalysis Research and Application Center, 44280, Malatya,
Turkey
b Sinop University, Scientific and Technological Research Application and Research
Center, 57010, Sinop, Turkey
c Ondokuz Mayıs University, Department of Physics, 55139, Samsun, Turkey
Appl. Organometal. Chem. (2016)
Copyright © 2016 John Wiley & Sons, Ltd.

E. Ö. Karaca et al.
short silica column (ethyl acetate as eluent) and was then concen-
trated under reduced pressure. After purification by flash chroma-
tography (ethyl acetate–hexane as eluent), the yield was
calculated based on anilines.
Experimental
Materials
All reactions for the preparation imidazolinium salts and palladium–
N-heterocyclic carbene complexes (1) were carried out under argon
in flame-dried glassware using standard Schlenk techniques. The
solvents used were purified by distillation over the drying agents
indicated and were transferred under argon: tetrahydrofuran,
Characterization
Melting point determination
2 2 2 4
Et O (Na/K alloy), CH Cl (P O10), hexane, toluene (Na). Glassware
was heat-dried in vacuum. Elemental analyses were performed by
the Turkish Research Council (Ankara, Turkey) Microlab.
Melting points were measured in open capillary tubes with an
Electrothermal-9200 melting point apparatus and are uncorrected.
IR spectroscopy
General procedure for preparation of palladium–N-
heterocyclic carbene complexes (1a–f)
Fourier transform IR spectra were recorded as KBr pellets in the
range 400–4000 cm using a ATI UNICAM 1000 spectrometer.
À1
[
20]
Imidazolinium salts were prepared according to the literature.
The palladium complexes were prepared by means of the Ag–
carbene transfer method developed by Wang and Lin. The silver
monocarbene complexes, which subsequently served as a carbene
NMR spectroscopy
1
13
H NMR and C NMR spectra were recorded using a Varian As 400
[
21]
1
13
Merkur spectrometer operating at 400 MHz ( H) or 100 MHz ( C) in
CDCl with tetramethylsilane as an internal reference. The NMR
studies were carried out using high-quality 5 mm NMR tubes.
Signals are quoted in parts per million downfield from tetrame-
thylsilane (0.00 ppm) as an internal standard. Coupling constants
3
transfer agents, were synthesized by the reaction of Ag O with 2
2
[
22]
equiv. of salts in CH Cl at ambient temperature.
We conve-
2
2
niently reacted in situ generated Ag–N-heterocyclic carbene with
PdCl (CH CN) in dark conditions and the mixture was allowed to
2
3
2
(J values) are given in hertz. NMR multiplicities are abbreviated as
stir for 24 h at room temperature. When this reaction was carried
out using a Ag:Pd ratio of 2:1, dichloro-bis(carbene) complexes
follows: s = singlet, d = doublet, t = triplet, m = multiplet signal.
1a–f were observed (Scheme 1). After filtration of AgCl, the solvent
Gas chromatography
was removed in vacuum to yield a pale yellow powder. The crude
product was recrystallized from dichloromethane–diethyl ether
All reactions were monitored using an Agilent 6890 N GC system by
GC-FID with an HP-5 column of 30 m length, 0.32 mm diameter and
(1:2) at room temperature.
0.25 μm film thickness.
Column chromatography
Typical procedure for catalytic C–N bond formation
t
Column chromatography was performed using silica gel 60 (70–230
mesh). Solvent ratios are given as v/v.
Under argon, 1.5 mmol of KOBu , 1 mol% of catalyst, 1 mmol of
amine, 1.2 mmol of bromobenzene and 2 ml of dimethoxyethane
were added into an oven-dried Schlenk tube. The mixture was
stirred at 80 °C for 15 h. The reaction mixture was allowed to cool
to room temperature and was quenched by filtering through a
X-ray diffraction
A suitable crystal of 1a was selected for data collection which was
performed using a STOE IPDS II diffractometer with graphite-
monochromatic Mo Kα radiation at 296 K. The structures were
[
23]
solved by direct methods using SHELXS-97 and refined by full-
2
[23]
matrix least-squares methods on F using SHELXL-97 from within
[
24]
the WINGX suite of software. All non-hydrogen atoms were re-
fined with anisotropic parameters. The hydrogen atoms were lo-
cated from different maps and then treated as riding atoms with
C–H distances of 0.93–0.97 Å. Molecular diagrams were created
using MERCURY. Details of data collection and crystal structure
determinations are given in Table 1. The molecular structure of 1a
with the atom labelling is shown in Fig. 1.
[25]
Dichlorobis[1,3-bis(2-methylbenzyl)imidazolidin-2-yliden]palladium(II) (1a)
1
H NMR (CDCl
3
, δ, ppm): 2.34 (s, 6H, CH
(CH
, δ, ppm): 19.6 (CH
(CH )-2), 126.3 (CH, C
), 133.9 (Cipso, C ), 136.7 (Cipso
), 198.8 (Pd–Ccarb). Anal. Calcd for C38 70Cl Pd: C, 60.03; H,
2
C
6
H
4
(CH
)-2), 7.08–7.56 (m, 8H,
(CH )-
), 127.7
3
)-2), 3.32 (s, 4H,
NCH
CH
), 48.1 (NCH
CH, C ), 129.3 (CH, C
2
CH N), 5.25 (s, 4H, CH
2
2
C
6
H
4
3
1
3
2 6
C
H
4
(CH
3
)-2). C{H}NMR (CDCl
CH N), 51.5 (CH
), 130.3 (CH, C
3
C H
2 6 2
3
2
(
C
2
2
2
C
6
H
4
3
5
4
6
3
2
,
1
H
2 4
N
9.28; N, 7.37. Found (%): C, 60.08; H, 9.21; N, 7.33.
Dichlorobis[1,3-bis(4-methylbenzyl)imidazolidin-2-yliden]palladium(II) (1b)
1
H NMR (CDCl
3
, δ, ppm): 2.33 (s, 6H, CH
(CH
, δ, ppm): 21.2 (CH
2
C
6
H
4
(CH
)-4), 7.11–7.25 (m, 8H,
(CH )-
3
)-4), 3.49 (s, 4H,
NCH
CH
2
CH N), 5.24 (s, 4H, CH
2
2 6
C
H
4
3
13
Scheme 1. Synthesis of Pd–N-heterocyclic carbene complexes.
2 6 4 3
C H (CH )-4). C{H}NMR (CDCl
3
C H
2 6 2
3
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Copyright © 2016 John Wiley & Sons, Ltd.
Appl. Organometal. Chem. (2016)

Palladium–NHC complexes as amination catalysts
Table 1. Crystal data and structure refinement parameters for 1a
Dichlorobis[1,3-bis(4-i-propylbenzyl)imidazolidin-2-yliden]palladium(II) (1d)
1
Empirical formula
38 2 4
C H44Cl N Pd
H NMR (CDCl , δ, ppm): 1.26 (d, J = 6.9 Hz, 12H, CH C H (CH(CH ) )-
3
2
6
4
3 2
4
), 2.90 (h, J = 6.9 Hz, 2H, CH C H (CH(CH ) )-4), 3.41 (s, 4H,
2 6 4 3 2
Formula weight
Crystal system
Space group
a (Å)
734.07
NCH CH N), 5.25 (s, 4H, CH C H (CH(CH ) )-4), 7.17–7.49 (m, 8H,
CH C H (CH(CH ) )-4). C{H}NMR (CDCl , δ, ppm): 24.0 (CH C H
2
2
2
6
4
3 2
Monoclinic
P21/c
13
2
6
4
3 2
3
2 6 2
(CH(CH ) )-4), 33.8 (CH C H (CH(CH ) )-4), 47.6 (NCH CH N), 54.0
3 2 2 6 2 3 2 2 2
7.8688(2)
14.5408(4)
16.0025(4)
90.536(2)
1830.90(8)
2
(CH C H (CH(CH ) )-4), 126.8 (CH, C3,5), 128.8 (CH, C2,6), 129.8 (Cipso
,
2
6
4
3 2
b (Å)
C1), 148.9 (Cipso, C ), 197.9 (Pd–C ). Anal. Calcd for C H Cl N Pd
4
carb
46 86
2 4
c (Å)
(%): C, 63.32; H, 9.93; N, 6.42. Found (%): C, 63.38; H, 9.99; N, 6.47.
β (°)
V (Å )
3
Dichlorobis[1,3-bis(4-diethylaminobenzyl)imidazolidin-2-yliden]palladium(II)
1e)
(
Z
À3
D
c
(g cm
)
1.332
1
H NMR (CDCl
CH CH –4), 3.50 (q, J = 7.2 Hz, 8H, CH
s, 4H, NCH CH N), 5.30 (s, 4H, CH
.44 (d, J = 8.4 Hz, 8H, CH
δ, ppm): 15.3 (CH N(CH
3
, δ, ppm): 1.23 (t, J = 6.9 Hz, 12H, CH
N(CH CH –4), 5.14
N(CH CH –4), 6.64 and
–4). C{H}NMR (CDCl
–4), 44.4 (CH N(CH CH
N(CH CH –4), 111.8 (CH, C3,5),
), 147.3 (Cipso, C ), 197.1 (Pd–Ccarb).
Pd (%): C, 62.26; H, 7.73; N, 11.62. Found
%): C, 62.22; H, 7.78; N, 11.66.
2 6 4
C H N
À1
μ (mm
)
0.68
(
(
7
2
)
3 2
C H
2 6 4
2
3 2
)
θ range (°)
Measured reflections
1.9–28.1
27 322
2
2
2
C
6
H
CH
4
2
3 2
)
13
C H
2 6 4
N(CH
2
3
)
2
3
,
Independent reflections
3792
C H
2 6 2
CH )
2 3 2
C H
2 6 2
2
3 2
) –
R
S
R
int
0.025
4
1
), 47.5 (NCH
22.8 (CH, C2,6), 130.3 (Cipso, C
74Cl
CH N), 53.8 (CH C H
2 2 2 6 4
2
3 2
)
1.05
1
4
1
/wR
2
0.025/0.064
0.39/À0.25
Anal. Calcd for C50
(
H
2 8
N
À3
Δρmax/Δρmin (e Å
)
Dichlorobis[1,3-bis(3,4-dimethoxybenzyl)imidazolidin-2-yliden]palladium(II) (1f)
4
), 47.8 (NCH
2
CH
2
N), 54.8 (CH
2
C
6
H
4
(CH
3
)-4), 128.8 (CH, C3,5), 129.0
), 197.9 (Pd–Ccarb). Anal.
Pd (%): C, 60.03; H, 9.28; N, 7.37. Found (%):
1
H NMR (CDCl
–3), 3.85 (s, 6H, CH
–3,4), 6.75–7.41 (m, 6H, CH
, δ, ppm): 47.4 (NCH CH N), 53.6 (CH
(OCH –4), 56.3 (CH (OCH –3,4), 110.7 (CH, C
3
, δ, ppm): 3.40 (s, 4H, NCH
2
CH
2
N), 3.49 (s, 6H, CH
2
C
6
H
H
3
3
(CH, C2,6), 132.9 (Cipso, C
1 4
), 134.7 (Cipso, C
(
(
(
(
OCH
OCH
CDCl
CH
3
)
2
C H (OCH
2 6 3 3 2
) –4), 5.31 (s, 4H, CH
2
C
6
Calcd for C38 70Cl
C, 60.09; H, 9.22; N, 7.33.
H
N
2 4
13
3
)
2
2 6
C H
3
(OCH
3
)
H
2
–3,4). C{H}NMR
(OCH –3), 55.9
),
3
2
2
2
C
6
3
3 2
)
2
C
6
H
3
)
3 2
C H
2 6 3
3
)
2
5
Dichlorobis[1,3-bis(4-ethylbenzyl)imidazolidin-2-yliden]palladium(II) (1c)
2 6 ipso 1
111.8 (CH, C ), 121.0 (CH, C ), 128.5 (C , C ), 148.7 (Cipso, C4),
1
49.4 (Cipso, C
3 2 4 8
), 197.0 (Pd–Ccarb). Anal. Calcd for C42H54Cl N O Pd
1
H NMR (CDCl
3
, δ, ppm): 1.24 (t, J = 7.8 Hz, 6H, CH
.66 (q, J = 7.8 Hz, 4H, CH (CH CH )-4), 3.39 (s, 4H, NCH
.42 (s, 4H, CH (CH CH )-4), 7.18 and 7.43 (d, J = 7.8 Hz, 8H,
(CH CH )-4). C{H}NMR (CDCl , δ, ppm): 15.4 (CH
)-4), 28.6 (CH (CH CH )-4), 47.5 (NCH CH N), 54.1
(CH CH )-4), 128.0 (CH, C3,5), 128.9 (CH, C2,6), 132.5 (Cipso
), 144.0 (Cipso, C ), 174.3 (Pd–Ccarb). Anal. Calcd for C42 53Cl Pd
%): C, 63.76; H, 6.75; N, 7.08; Found (%): C, 63.70; H, 6.71; N, 7.01.
2 6
C
H
4
(CH
2
CH
3
)-4),
(%): C, 49.00; H, 5.29; N, 5.44. Found (%): C, 49.05; H, 5.34; N, 5.40.
2
5
CH
CH
CH
C
2
C
6
H
4
2
3
2
CH
2
N),
2
C
6
H
4
2
3
1
3
C H
2 6 4
2
3
3
2 6 2
C H
Results and discussion
(
(
2
CH
3
2
C
6
H
2
2
3
2
2
C H
2 6 4
2
3
,
The procedure involving Ag–N-heterocyclic carbene, generated by
treatment of imidazolium salt with Ag O, is probably one of the
2
most general methods, because it generates an air-stable interme-
diate under mild reaction conditions. It is often used successfully
1
4
H
2
N
4
(
[26]
when other methods fail. The use of Ag–N-heterocyclic carbene
complexes as carbene transfer reagents provides in many cases a
convenient way to overcome the difficulties arising from using
strong bases, inert atmospheres and complicated workups. This
method was used for the preparation of complexes 1a–f. Firstly,
we examined the formation of variously substituted Ag–N-
heterocyclic carbene complexes having two aryls on the N-
heterocyclic carbene moiety. All these Ag–N-heterocyclic carbene
[
22]
compounds were obtained in high yields.
The isolated Ag–N-
heterocyclic carbene complexes were converted into yellow Pd–
N-heterocyclic carbene complexes (1a–f) in high yields (Scheme 1).
The air- and moisture-stable palladium carbene complexes 1a–f
are soluble in solvents such as dichloromethane and chloroform,
and insoluble in nonpolar solvents. The complexes 1a–f, which
are very stable in the solid state, were characterized using
analytical and spectroscopic techniques. Palladium complexes
À1
exhibit a characteristic ν(NCN) band typically at 1515–1542 cm
13
for 1a–f. C NMR chemical shifts provide a useful diagnostic tool
for this type of metal carbene complex. The chemical shifts for the
carbon atom fall in the range 174.3–198.8 ppm and are similar to
those found for other palladium–carbene complexes. These com-
plexes show typical spectroscopic signatures, which are in line
Figure 1. Molecular structure of 1a showing the atom numbering scheme
(i) –x + 1, Ày + 1, Àz + 1). Selected bond lengths (Å) and angles (°): Pd1–
C11 = 2.0247(17), C11–N1 = 1.322(2), C11–N2 = 1.329(2), Cl1–Pd1 = 2.2997
5), C11–Pd1–Cl1 88.04(5), C11–Pd1–Cl1 91.96(5), N2–C11–
(
(
=
=
Pd1 = 124.29(13), N1–C11–Pd1 = 127.00(13).
2
with those recently reported for other [PdCl (N-heterocyclic
Appl. Organometal. Chem. (2016)
Copyright © 2016 John Wiley & Sons, Ltd.
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E. Ö. Karaca et al.
Table 2. Analytical data for Pd–N-heterocyclic carbene complexes
1
13
Complex
Yield
%)
M.p.
(°C)
ν
(cm
(NCN)
H NMR δ (ppm)
NCH CH NNCH Ar
C NMR δ
À1
(
)
2
2
2
Ccarb (ppm)
1
1
1
1
1
1
a
b
c
90
95
92
94
91
93
226–227
269–270
272–273
242–243
234–235
200–201
1526
1527
1540
1542
1518
1515
3.32
5.25
198.8
197.9
174.3
197.9
197.1
197.0
3.49
3.39
3.41
3.40
3.40
5.24
5.42
5.25
5.30
5.31
d
e
f
[18,19,27]
2
carbene) ] complexes.
The analytical data are in good
Catalytic C–N bond formation
agreement with the compositions proposed for all the complexes
and are summarized in Table 2.
Amines are important building blocks possessing wide application in
agrochemicals, fine chemical industries, pharmaceuticals, materials
[28–32]
science and biotechnology.
As a consequence, a number of
[33–38]
research groups have devoted efforts towards their synthesis.
Molecular Structure
The Buchwald–Hartwig amine arylation reaction is a useful and
versatile method to obtain aryl amines and so it has great interest
in modern synthetic chemistry. These protocols provide access to a
range of hindered and functionalized drug-like arylamines in high
yield with both electron-deficient and electron-rich aryl and
heteroaryl chlorides and bromides.
From the outset our aim was to develop an effective, user-friendly
and easily implemented process requiring only general laboratory
techniques to carry out the amination protocol. Therefore, we
initiated a study focusing on the catalytic activity of new Pd–N-
heterocyclic carbene complexes for aryl amination using
A single crystal of 1a suitable for X-ray analysis was obtained by
slow diffusion of diethyl ether into dichloromethane at room
temperature. The crystal and molecular structure of complex 1a
was confirmed using single-crystal X-ray diffractometry. Its molecu-
lar structure is depicted in Fig. 1 with selected bond lengths and
angles. The X-ray structure shows a square planar geometry around
the palladium and the palladium centre in the complex is coordi-
nated by two chloro ligands and two N-heterocyclic carbene
ligands in a trans position. The bond length between C and Pd is
2.0247 Å.
Table 3. Coupling reaction of anilines or amines with aryl bromide
Entry
Product
R
Yield (%)
1
a
1b
1c
1d
1e
1f
a
1
A
H
Me
OMe
H
71
76
81
84
87
90
80
86
91
92
92
86
83
87
88
81
85
80
68
75
89
83
84
83
77
78
90
86
89
85
78
89
87
87
81
82
a
2
A
a
3
A
b
4
B (n = 0)
B (n = 1)
B (n = 2)
b
5
H
b
6
H
t
a
b
Reaction conditions: catalyst 1a–f (0.01 mmol), KOBu (1.5 mmol), amine (1 mmol), aryl bromide ( 2.4 mmol; 1.2 mmol), dimethoxyethane (2 ml), 80 °C,
15 h. Yields are based on anilines. All reactions were monitored by GC and GC–MS.
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Palladium–NHC complexes as amination catalysts
bromobenzene and various anilines or amines. As a starting point,
the coupling of aniline with bromobenzene was selected as a model
reaction. In a typical experiment the preformed, isolated catalyst
allow the preparation of a range of structurally intriguing,
drug-like aromatic amines. The catalyst system was applied to
the reactions of various anilines and amines with bromobenzene.
The present system was found to lead to efficient amination. Our
continuing studies in this area will examine the utility of
N-heterocyclic carbene ligands in other challenging metal-
catalysed reactions.
(0.01 mmol) was dissolved in solvent (2 ml). After the catalyst had
completely dissolved, amine (1.00 mmol), aryl bromide (2.4 mmol)
and a base (1.5 mmol) were added and the reaction was performed
at 80 °C. The reactions were conducted using an amine/catalyst/base
molar ratio of 1:0.01:1.5.
The choice of base has often been found to be critical. Alkoxide
base acts as an initiator in the present system, leading to the
formation of a palladium alkoxide species that is subsequently
transformed via a mechanism proposed by Alcazar-Roman and
Acknowledgements
This work was financially supported by the Technological and
Scientific Research Council of Turkey TUBİTAK-BOSPHORUS
[39]
(France) [109T605] and İnönü University Research Fund (İÜBAP:
Hartwig.
sodium and potassium tert-butoxide, though weaker bases (e.g.
The most successful and widely utilized bases are
2014/32-Güdümlü).
[40]
t
Cs CO ) have also been employed. We preferred to use KOBu
2
3
because of observed higher conversions. The amination product
was obtained in not more than 20% yield when K CO and Cs CO
were used as bases.
2
3
2
3
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Appl. Organometal. Chem. (2016)