A new palladium(II) complex of a functionalized N-heterocyclic carbene: Synthesis, characterization and application in Suzuki-Miyaura cross-coupling reactions

Article abstract of DOI:10.1016/j.molstruc.2008.05.037

trans-[PdBr₂(NHC)Im] was prepared by reacting the corresponding imidazolium (Im) salt with palladium(II) acetate in dimethylsulfoxide in an in-situ reaction without generating a free carbene. Both the salt and the complex were characterized spectroscopically and by X-ray structure analysis. The complex was tested in homogeneous Suzuki-Miyaura cross-coupling reactions.

Full text of DOI:10.1016/j.molstruc.2008.05.037

Journal of Molecular Structure 890 (2008) 192–197
Contents lists available at ScienceDirect
Journal of Molecular Structure
journal homepage: www.elsevier.com/locate/molstruc
A new palladium(II) complex of a functionalized N-heterocyclic carbene:
Synthesis, characterization and application in Suzuki–Miyaura cross-coupling
reactions
Claudia S. Linninger a, Eberhardt Herdtweck a, Stephan D. Hoffmann b, Wolfgang A. Herrmann a,
Fritz E. Kühn a,c,
*
a Lehrstuhl für Anorganische Chemie, Fakultät für Chemie, Technische Universität München, Lichtenbergstraße 4, 85747 Garching, Germany
b Lehrstuhl für Anorganische Chemie mit Schwerpunkt Neue Materialien, Fakultät für Chemie, Technische Universität München, Lichtenbergstraße 4, 85747 Garching, Germany
c Molekulare Katalyse, Fakultät für Chemie, Technische Universität München, Lichtenbergstraße 4, 85747 Garching, Germany
a r t i c l e i n f o
a b s t r a c t
Article history:
trans-[PdBr2(NHC)Im] was prepared by reacting the corresponding imidazolium (Im) salt with palla-
dium(II) acetate in dimethylsulfoxide in an in-situ reaction without generating a free carbene. Both the
salt and the complex were characterized spectroscopically and by X-ray structure analysis. The complex
was tested in homogeneous Suzuki–Miyaura cross-coupling reactions.
Received 24 January 2008
Received in revised form 18 May 2008
Accepted 19 May 2008
Available online 3 June 2008
Ó 2008 Elsevier B.V. All rights reserved.
Keywords:
Imidazolium salt
N-heterocyclic carbene
Palladium
Suzuki–Miyaura cross-coupling
1. Introduction
The synthesis and structural characterization of a new imidazo-
lium salt and a Pd(II) NHC complex containing a functional group
Since the first synthesis of N-heterocyclic carbene complexes by
Öfele [1] and, independently, by Wanzlick and Schönherr [2] in the
1960s and the isolation of free carbenes by Arduengo et al. [3] in
1991, N-heterocyclic carbenes (NHC) gained remarkable attention.
that could facilitate immobilization is herein reported.
2. Experimental
Because of their strong
r-donor character and low toxicity, they
Unless otherwise stated, all reactions were performed under a
dry argon atmosphere using standard Schlenk techniques. Solvents
and substrates were dried by standard procedures, distilled under
an argon atmosphere and stored over molecular sieves. 2,3-Dib-
romopropionic-acid ethylester and dimethylsulfoxide were pur-
chased from Acros and used without further purification. 1H and
13C{1H} NMR spectra were recorded on a JEOL-JMX-GX 400 MHz
spectrometer at room temperature. 1H NMR peaks are labeled as
singlet (s), doublet (d), triplet (t), quartet (q). Mass spectrometric
measurements were performed on a Finnigan MAT 90 spectrome-
ter using the FAB technique. Elemental analyses were executed in
the Microanalytical Laboratory at the TU München. GC spectra
were measured on a Varian gas chromatograph CP 3800 equipped
with a FID detector.
are considered as alternatives to phosphine ligands in metal com-
plexes [4]. Many such metal complexes containing NHC ligands
have been synthesized and applied as catalysts. They do not only
show excellent activities in CAC-coupling reactions such as the
Heck reaction [5] and the Sonogashira reaction [6], they have also
been shown to be active in carbon monoxide/ethylen copolymeri-
sation [7]. There is a significant interest in functionalized NHC li-
gands to be utilized for the immobilization of complexes to
combine the advantages of homogeneous and heterogeneous catal-
ysis. One possibility for immobilization is via attached ester
groups.
2.1. 1-(30-Ethoxycarbonylethenyl)-3-methylimidazoliumbromide (1)
* Corresponding author. Address: Molekulare Katalyse, Fakultät für Chemie,
Technische Universität München, Lichtenbergstraße 4, 85747 Garching, Germany.
Fax: +49 89 289 13473.
E-mail addresses: wolfgang.herrmann@ch.tum.de (W.A. Herrmann), fritz.
kuehn@ch.tum.de (F.E. Kühn).
In an ACE pressure tube 1.168 g (14.22 mmol) 1-methylimidaz-
ole and 1.948 g (7.49 mmol) 2,3-dibromopropionic-acid ethylester
0022-2860/$ - see front matter Ó 2008 Elsevier B.V. All rights reserved.
doi:10.1016/j.molstruc.2008.05.037

C.S. Linninger et al. / Journal of Molecular Structure 890 (2008) 192–197
193
Table 1
are dissolved in 5 mL acetonitrile at room temperature. After stir-
Crystallographic data for compounds 1 and 2
ring the solution for 16 h, the reaction mixture is heated to
120 °C for another 16 h. After cooling to room temperature the
resulting precipitate is filtered off and washed twice with 5 mL
THF. Evaporation of the solvent under reduced pressure leaves
compound 1 as a light brown solid. The product is recrystallized
from THF, yielding 0.4 g (20%) of light yellow crystals.
1
2
Formula
Fw
C9H13BrN2O2
261.11
C13H18Br2N4O2Pd
528.53
Orange/plate
0.18 ꢁ 0.20 ꢁ 0.33
Triclinic
P1 (no. 2)
8.5435(1)
9.6629(2)
12.1424(2)
102.5404(9)
92.4640(9)
112.2703(7)
896.76(3)
2
Color/habit
Crystal dimensions (mm3)
Crystal system
Space Group
a (Å)
Light yellow/plate
0.20 ꢁ 0.50 ꢁ 0.80
Monoclinic
P21/n (no. 14)
7.860(2)
13.671(3)
10.848(3)
90
108.36(3)
90
1106.3(5)
4
Anal. Calc. for C9H13BrN2O2 (261.11): C 41.40; H 5.02; N 10.73.
Found: C 40.69; H 5.17; N 11.07. MS (FAB): m/z (%) 181, [M-Br]+
(100); 1H NMR (400 MHz, 298 K, d6-DMSO): d = 9.64 (1H, s, NCHN),
b (Å)
c (Å)
3
8.34 (1H, s, NCH), 8.25 (1H, d, JHH = 14 Hz, C@CH), 7.92 (1H, s,
3
a
(°)
NCH), 6.89 (1 H, d, JHH = 14 Hz, C@CH), 4.23 (2 H, q, OCH2), 3.92
b (°)
(3 H, s, NCH3), 1.27 (3 H, t, CH2CH3). 13C{1H} NMR (100 MHz,
298 K, d6-DMSO): d = 165.1 (C@O), 138.7 (NCHN), 136.5 (C@C),
125.6 (NCH), 120.4 (NCH), 113.7 (C@C), 61.5 (OCH2), 36.9 (NCH3),
14.6 (CH2CH3).
c
(°)
V (Å3)
Z
T (K)
150
1.568
3.694
528
173
1.957
5.501
512
Dcalcd (g cmꢀ3
)
l
(mmꢀ1
)
2.2. Dibromo[3-methylimidazol][(1-(3’-ethoxycarbonylethenyl)-3-
F(000)
methyl-imidazolin-2-yliden)]palladium(II) (2)
h Range (°)
Index ranges (h,k,l)
No. of rflns. collected
No. of indep. rflns./Rint
No. of obsd. rflns. (I > 2
3.11–25.37
9, 16, 13
12,935
2019/0.027
1618
2019/0/179
0.0223/0.0513
0.0337/0.0529
0.954
1.73–25.31
10, 11, 14
16,150
3279/0.034
3020
3279/0/202
0.0196/0.0432
0.0228/0.0444
1.043
Palladium(II)acetate (53 mg, 0.24 mmol) and 1-(30-ethoxycar-
bonylethenyl)-3-methylimidazoliumbromide (63 mg, 0.24 mmol)
are dissolved in 5 mL DMSO. After stirring for 3 h at 50 °C, the solu-
tion is heated to 90 °C for 1 h. The solvent is removed under vac-
uum and the residue is stirred with 10 mL THF. The solution is
filtered off and the solvent is evaporated under vacuum, yielding
57 mg (46%) of an orange powder. Re-crystallization in THF yields
orange crystals.
r
(I))
No. of data/restraints/params
R1/wR2 (I > 2r
(I))a
R1/wR2 (all data)a
GOF (on F2)a
Largest diff. peak and hole (e Åꢀ3
)
+0.44/ꢀ0.40
+0.35/ꢀ0.45
P
P
P
P
2
2
1=2
R1
¼
ðkFo j ꢀ j FckÞ= j Fo j; wR2 ¼ f ½wðF2o ꢀ Fc2Þ ꢂ= ½wðFo2Þ ꢂg
;
GOF ¼
a
P
2
1=2
f
½wðF2o ꢀ F2c Þ ꢂ=ðn ꢀ pÞg
.
Anal. Calc. for C13H18Br2N4O2Pd (M = 528.53): C 29.54; H 3.43; N
10.60. Found: C 29.76; H 3.68; N 10.29. MS (FAB): m/z (%) 448 (20,
[M-Br]), 366 (20, [M-Br-C4H6N2]), 181, 136 (100), 154 (85); 1H
NMR (400 MHz, 298 K, d6-DMSO): d = 8.75 (1H, s, NCHN), 8.12
system,
j
-CCD; sealed tube, Enhance X-ray Source, Spellman
DF3; five data sets in rotation scan modus with
D
u/Dx = 2.0°;
3
dx = 60; T = 150 K. Intensities were integrated and the raw data
were corrected for Lorentz polarization and, arising from the scal-
ing procedure, for latent decay and absorption effects. The struc-
tures were solved by a combination of direct methods and
difference Fourier syntheses. All non-hydrogen atoms were refined
with anisotropic displacement parameters. Hydrogen atoms were
solved by difference Fourier syntheses and refined with isotropic
displacement parameters. Full-matrix least-squares refinements
(1H, d, JHH = 15.9 Hz, C@CH), 8.09 (1H, s, NCH), 7.62 (1H, s, NCH),
3
7.29 (1H, s, NCH), 7.18 (1H, s, NCH), 6.71 (1H, d, JHH = 15.9 Hz,
C@CH), 4.20 (2H, q, OCH2), 3.95 (3H, s, NCH3), 3.68 (3H, s, NCH3),
1.26 (3H, t, CH2CH3); 13C{1H} NMR (100 MHz, 298 K, d6-DMSO):
d = 165.5 (C@O), 156.7 (CCarben), 140.3 (C@C), 140.4 (NCHN), 128.6
(NCH), 126.0 (NCH), 121.1 (NCH), 119.4 (NCH), 108.7 (C@C), 60.7
(OCH2), 39.1 (NCH3), 34.0 (NCH3), 14.2 (CH2CH3).
P
2
were carried out by minimizing
97 weighting scheme and stopped at shift/err <0.001. The final
residual electron density maps showed no remarkable features.
wðF2o ꢀ F2c Þ with the SHELXL-
2.3. Catalysis
Suzuki–Miyaura reaction. Phenylboronic acid (1.20 mmol) and
potassium carbonate (1.50 mmol) were placed in a Schlenk tube
equipped with a stirring bar under argon. Aryl halide (1.00 mmol),
100 mg diethylene glycol/di-n-butyl ether as internal standard and
5 mL degassed solvent were added. After thermostating for 10 min
at the temperature given in Table 3, the catalyst solution was
added under argon. To end the reaction, the mixture was cooled
to room temperature and 5 mL of water were added. The water
phase was extracted three times with 2 mL of diethyl ether and
the organic phases dried with MgSO4.
2.4.2. Single crystal X-ray structure determination of compound 2
Crystal data and details of the structure determination of com-
pound 2 are presented in Table 1. Suitable single crystals for the X-
ray diffraction study were grown from THF. A clear orange frag-
ment was stored under perfluorinated ether, transferred in a Linde-
mann capillary, fixed and sealed. Preliminary examination and
data collection were carried out on an area detecting system (Non-
ius, Mach3,
j
-CCD) at the window of a rotating anode (Nonius,
Fr591) and graphite monochromated Mo-K
radiation
a
(k = 0.71073 Å). The unit cell parameters were obtained by full-ma-
trix least-squares refinement of 3276 reflections. Data collection
were performed at 173 K (Oxford Cryosystems) within a h-range
of 1.73° < h < 25.31°. Measured each with eight data sets in rotation
2.4. Single crystal X-ray structure, determinations
2.4.1. Single crystal X-ray structure determination of compound 1
Details of the X-ray experiment, data reduction and final struc-
ture refinement calculation of compound 1 are summarized in Ta-
ble 1. Suitable single-crystals for the X-ray diffraction study were
selected under perfluorinated ether and fixed on a glass capillary.
Preliminary examination and data collection were carried out on
scan modus with
Du/Dx = 2.0°. A total number of 16,150 intensi-
ties were integrated. Raw data were corrected for Lorentz polariza-
tion and, arising from the scaling procedure, for latent decay and
absorption effects. After merging [Rint = 0.034 a sum of 3279 (all
data) and 3020 [I > 2r (I)], respectively, remained and all data were
an area detecting system and graphite-monochromated Mo-K
a
used. The structures were solved by a combination of direct meth-
ods and difference Fourier syntheses. All non-hydrogen atoms
were refined with anisotropic displacement parameters. All
hydrogen atoms were placed in ideal positions (riding model).
radiation (k = 0.71073 Å). The unit cell parameters were obtained
by full-matrix least-squares refinements during the scaling proce-
dure. Data collections were performed at low temperatures (Ox-
ford Diffraction cooling device) on a Oxford Diffraction Xcalibur3

194
C.S. Linninger et al. / Journal of Molecular Structure 890 (2008) 192–197
Table 2
Selected bond distances (Å) and angles (°) for compounds 1 and 2
1
2
N1AC1
N1AC2
N1AC4
N2AC1
N2AC3
N2AC5
C2AC3
PdABr1
PdABr2
PdAN3
PdAC1
1.320(3)
1.385(3)
1.463(3)
1.342(3)
1.388(3)
1.415(3)
1.337(3)
1.337(3)
1.386(4)
1.457(3)
1.369(3)
1.394(3)
1.404(3)
1.333(4)
2.4277(3)
2.4362(3)
2.100(3)
1.962(3)
Scheme 1. Synthesis of compound 1.
Full-matrix least-squares refinements with 202 parameters were
P
2
carried out by minimizing
wðF2o ꢀ F2c Þ with the Shelxl-97
weighting scheme and stopped at shift/err <0.001. The final resid-
ual electron density maps showed no remarkable features. Neutral
atom scattering factors for all atoms and anomalous dispersion
corrections for the non-hydrogen atoms were taken from Interna-
tional Tables for Crystallography. All calculations were performed
on an Intel Pentium 4 PC, with the WinGX system, including the
programs Diamond, Platon, Shelxl-97, and Sir92 [8].
N1AC1AN2
C1AN1AC2
C1AN1AC4
C1AN2AC3
C1AN2AC5
Br1APdABr2
Br1APdAN3
Br1APdAC1
Br2APdAN3
Br2APdAC1
N3APdAC1
107.8(2)
109.5(2)
124.3(2)
108.5(2)
126.4(2)
105.0(2)
110.9(2)
125.0(2)
110.1(2)
124.2(2)
174.30(1)
93.13(6)
88.29(8)
92.14(6)
86.50(7)
178.1(1)
3. Results and discussion
Ligand attached ester groups have been successfully utilized for
immobilization purposes of other catalysts before, usually
accounting for quite low leaching [9]. This concept was applied
to synthesize a novel carbene complex. This complex was tested
in homogeneous Suzuki–Miyaura cross-coupling reactions.
C1AH1
Br. . .H1
Br’. . .H1
Br. . .H1. . .Br’
H1. . .Br. . .H1’
0.94
2.818
2.773
103.4
76.6
3.1. Synthesis and characterization
methanol and dimethylsufoxide and is stable both under air and in
the presence of moisture.
The donor functionalized imidazolium bromide 1 was prepared
by reaction of 2,3-dibromopropionic-acid ethylester with N-meth-
ylimidazole in acetonitrile (Scheme 1). Only one halide atom was
substituted by N-methylimidazole. The other halide was elimi-
nated as HBr, resulting in a double bond. After crystallization in
THF, light yellow crystals were obtained and characterized by 1H
and 13C NMR spectroscopy, elemental analysis, MS and X-ray struc-
ture analysis. The salt is soluble in common polar solvents such as
The formation of compound 1 was verified by the appearance of
the NCHN peak at 9.64 ppm in the 1H NMR spectra. The single crys-
tal X-ray examination of compound 1 (Fig. 1) reveals an all-trans
alignment of the aliphatic side group bonded to N2, which is also
reflected in the 1H NMR spectra, where the coupling constant of
the protons connected to the C@C double bond is found to be
14 Hz. This is in a typical order of magnitude for protons in a trans
arrangement. The geometric parameters for the X-ray structure of
Fig. 1. ORTEP style plot [8 h] of compound 1 showing the basic hydrogen bonds in the solid state. A centre of symmetry is indicated by a dot. Symmetry related atoms are
generated by the operation (2 ꢀ x, ꢀy, 1 ꢀ z). Thermal ellipsoids are drawn at a 50% probability level.

C.S. Linninger et al. / Journal of Molecular Structure 890 (2008) 192–197
195
reported by Mas-Marzá et al. [11] N-heterocyclic precursors can
facilitate the cleavage of a CAN bond under mild conditions, yield-
ing the N-methylimidazole fragment.
The molecular geometry of complex 2 determined by a single
crystal X-ray experiment revealed a square-planar core geometry
around the Pd atom (Fig. 2). The carbene and N-methylimidazole
ligands display a trans arrangement, which is also reflected in the
proton NMR spectra, where the coupling constant of the protons
connected to the C@C double bond is found to be 15.9 Hz, being
a typical value for protons in a trans arrangement. The geometric
parameters for the X-ray structure of 2 are given in Table 2. The
N-methylimidazole ligand was found to coordinate to the metal
through the free electron pair of the N1-atom. The formation of
the carbene complex was established by the presence of a peak
at d(13C) = 156.7 ppm, which can be assigned to the 2C-imidazol-
2-ylidene (carbene) carbon. The signal is positioned upfield of the
characteristic shift of 175–186 ppm for carbene ligands trans to
another carbene [12,13]. The absence of a downfield peak for the
2H-imidazolium proton in the 1H NMR spectra usually observed
in non protic solvents below d(1H) = 9 ppm is also in accord with
the determined structure.
Scheme 2. Synthesis of complex 2.
1 are given in Table 2. The three dimensional solid state structure
of compound 1 is dominated by two C1AH1ꢃ ꢃ ꢃBr contacts, both
shorter than the sum of the relevant van der Waals radii (C1ꢃ ꢃ ꢃBr
3.55 Å) [10] thus generating a bifurcated hydrogen bridge at H1.
Interconnected via a centre of symmetry (black dot in Fig. 1) a di-
meric unit is created. On a larger scale this geometric motif is
three-dimensionally interconnected by two weaker Hꢃ ꢃ ꢃBr con-
tacts (C2AH2ꢃ ꢃ ꢃBr 3.706 and C5AH5ꢃ ꢃ ꢃBr 3.633 Å). The most acidic
proton in the molecule, H1, is fixed to the anion. Therefore the
chemical activity is reduced and the observed cleavage of the
CAN bond by reaction with palladium(II) acetate in DMSO as sol-
vent is obviously favored.
A palladium complex of the functionalized N-heterocyclic car-
bene 2 was prepared starting from palladium(II)acetate and two
equivalents of imidazolium salt 1 in dimethylsulfoxide (Scheme
2). The in-situ deprotonation of the imidazolium salt 1 leads to
the trans configured bromo palladium(II) complex 2, which is ob-
tained as orange crystals after recrystallization from THF. Complex
2 is both air- and moisture-stable and soluble in common polar sol-
vents such as DMSO or THF. However, instead of two carbenes
being connected to the metal centre just one carbene is attached
to the metal atom. The by-product of this reaction, N-methylimid-
azole, which is formed by the reaction of palladiumacetat with the
imidazolium salt, is connected to the metal centre via the N3 atom,
forming a square planar geometry around the palladium atom. As
To the best of our knowledge only one other palladium complex
with a similar trans-carben-N-methylimidazole-dihalogen metal
core has been structurally characterized and described before [6].
In the complex described herein, an ester group is in the side chain
instead of a ketone, making it possible to immobilize the complex
on a surface, e.g. on MCM-41.
3.2. Catalysis
Catalytic reactions were carried out by employing standard
conditions with arylbromides (Table 3), phenyl boronic acid
and potassium carbonate as base to enable an easy comparison
of the performance of our system with literature known cata-
lysts [14,15].
Fig. 2. ORTEP style plot [8] of compound 2 in the solid state. Thermal ellipsoids are drawn at a 50% probability level.

196
C.S. Linninger et al. / Journal of Molecular Structure 890 (2008) 192–197
Table 3
Selected results of Suzuki–Miyaura cross-coupling reactions of aryl halides (ArX, X = Br)
B(OH)2
Br
cat [Pd]
Base
+
R
R
Entry
mol% Pd
Reagent
Product
Time (h)
Yield (%)
TOF
Br
Br
Br
Br
Br
Ph
Ph
Ph
Ph
Ph
1
2
0.2
20
20
20
20
16
20
20
16
20
25
16
70
65
45
32
80
56
38
29
53
37
22
70
MeOC
MeOC
MeOC
MeOC
MeOC
MeOC
MeOC
MeOC
MeOC
MeOC
0.02
0.002
0.02
0.2
990
6700
250
75
3
4
5
Br
Br
Br
Ph
Ph
Ph
6
0.2
200
1300
10
7
0.02
0.2
8
Br
Ph
9
0.2
60
MeO
MeO
MeO
MeO
MeO
MeO
Ph
Ph
Br
Br
10
11
0.02
0.2
800
70
Reaction conditions: 1.00 mmol of aryl halide (ArX, X = Br), 1.2 mmol of phenyl boronic acid, 1.5 mmol of K2CO3 (entry 4: Cs2CO3), 5 ml of toluene, temperature = 110 °C
(entry 5,8,11: 5 ml of xylene, temperature = 130 °C). The yields were determined by GC using diethylene glycol/di-n-butyl ether as internal standard. TOFs have been
calculated from the conversion after 10 min.
The palladium complex 2 was found to be an efficient catalyst for
Suzuki–Miyaura cross-coupling reactions. The coupling of phenyl-
boronic acid and p-bromoacetophenone to yield 4-acetobiphenyl
wasachievedinhighyieldat110 °C(Table3). Astudyofthevariation
of catalyst loading was carried out in order to find the upper limit of
the catalyst efficiency and, in fact, a maximum turnover frequency of
ca. 6700 and 45% conversion after 20 h (Table 3, entry 3) were ob-
served by gas chromatography at 2 ꢁ 10ꢀ4 mol% of catalyst loading.
Further increase in the yield (80%) was achieved by increasing the
reaction temperature to 130 °C using xylene as solvent (Table 3, en-
try 5). Employing cesium carbonate instead of potassium carbonate
as base results in lower yields (Table 3, entry 4). Similar results were
obtained for coupling of phenylboronic acid with p-bromobenzene
yielding biphenyl as product (Table 3, entries 6, 7 and 8) and phenyl-
boronic acid with 4-bromoanisole yielding 4-methoxybiphenyl as
product (Table 3, entry 9, 10 and 11). High turnover frequencies up
to 1300 (Table 3, entry 7) respectively 800 (Table 3, entry 10) were
observed. Conversions of 38% (37%) at 2 ꢁ 10ꢀ2 mol% of catalyst
loading after 20 h (25 h) at 110 °C have been reached. Increasing
the reaction temperature leads to lower yields of the biphenyl, be-
cause by-products, observed by gas chromatography, are formed
(Table 3, entry 8 and 11).
For a better comparison of the relative catalyst activities the
time-conversion curves are shown in Fig. 3. The observed conver-
sions are within the range of previously described catalysts for Su-
zuki–Miyaura coupling [14,15]. Turnover frequencies had,
unfortunately, not been determined in most previous papers.
The synthesis and structural characterization of a new N-func-
tionalized imidazolium salt 1 and the corresponding Pd(II) com-
plex 2 has been herein reported. Preliminary investigations of the
performance of this novel palladium NHC complex in homoge-
neous CAC-coupling of arylhalides with phenyl boronic acid show
good activities. The ester functionality present in complex 2 could
be reacted with an amine, such as 3-amino-triethoxysilylpropane,

C.S. Linninger et al. / Journal of Molecular Structure 890 (2008) 192–197
197
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Fig. 3. Time-conversion-curves: Suzuki–Miyaura reaction. Entry 1 (}), entry 2 (j),
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Acknowledgements
C.S.L. thanks M.Sc. Evangeline Tosh, M.Sc. Alexandrina D. Tanase
and Dr. Karl Öfele for their fruitful discussions.