Palladium-catalyzed Heck reaction of aryl bromides in aqueous media using tris(N-heterocyclic carbene) ligands

Article abstract of DOI:10.1055/s-2007-973860

A highly effective, easy to handle and environmentally benign process for palladium-mediated Heck reaction was developed. The in situ prepared three-component system composed of palladium(II) acetate, a tris(azolinium) bromide and potassium tert-butoxide,

Full text of DOI:10.1055/s-2007-973860

LETTER
889
Palladium-Catalyzed Heck Reaction of Aryl Bromides in Aqueous Media
Using Tris(N-Heterocyclic Carbene) Ligands
a
a
b
H
I
eck
R
e
s
actionof
A
m
ryl Bromides ail Özdemir,* Serpil Demir, Bekir Çetinkaya
a
Inönü University, Faculty Science and Arts, Chemistry Department, 44280 Malatya, Turkey
Fax +90(422)3410212; E-mail: iozdemir@inonu.edu.tr
b
Department of Chemistry, Ege University, 35100 Bornova-Izmir, Turkey
Received 17 April 2006
Dedicated to Professor Richard F. Heck in great admiration of his scientific work as pioneer of organometallic and organic chemistry
number of reports of the palladium-mediated Heck reac-
tion being performed using water as solvents.9
Abstract: A highly effective, easy to handle and environmentally
benign process for palladium-mediated Heck reaction was devel-
oped. The in situ prepared three-component system composed of We have previously reported the use of an in situ formed
palladium(II) acetate, a tris(azolinium) bromide and potassium tert-
butoxide, quantitatively catalyzes the Heck reaction of aryl bro-
mides in aqueous media.
imidazolidin-2-ylidene, tetrahydropyrimidin-2-ylidene
and tetrahydrodiazepin-2-ylidenepalladium(II) systems
that exhibit high activity for various coupling reactions of
Key words: Heck reaction, imidazolinium and benzimidazolium
salts, C–C coupling, palladium, N-heterocyclic carbene
10
aryl bromides and aryl chlorides. In order to obtain more
stable, efficient and active systems, we have also investi-
gated benzoannelated derivatives.11 Recently, our group
reported that novel complexes of rhodium(I) 1,3-dialkyl-
imidazolidin-2-ylidenes gave secondary alcohols in good
yields by the addition of phenylboronic acid to alde-
Palladium-catalyzed arylation of olefins, the Heck reac-
1
tion, is a powerful tool in organic synthesis. It has found
widespread use in the synthesis of natural products, poly-
mers, dendrimers and various conjugated architectures of
interest in materials science. The Heck reaction also holds
much promise in many industrial processes, especially in
the synthesis of fine chemicals and active pharmaceutical
12
hydes. In this article, we wish to report an air and water
stable, effective tridentate NHC-ligated palladium cata-
lyst that can be used for activation of aryl bromides. Aim-
ing to find novel ligands for palladium-catalyzed
transformations, we synthesized a number of tridentate
imidazoliniums and benzimidazoliums as depicted in
Scheme 1. We report here an in situ Pd–carbene-based
2
intermediates. In view of these, much attention has been
paid in recent years to develop milder and operationally
simpler procedures for the Heck reaction. Some important
developments include the use of ligand-free palladium
catalysts in combination with tetraalkylammonium salts,
the use of palladacycles, pincer and supported palladium
catalysts and more recently the bulky electron-rich phos-
phine and N-heterocyclic carbene (NHC) ligands for pal-
13
catalytic system for the Heck reaction in aqueous media.
The 1-alkylimidazoline and 1-alkylbenzimidazole were
14
prepared according to known method. Tris(imidazoli-
dinium) bromides 2a–c, and tris(benzimidazolium) bro-
mides 3a–c are conventional NHC precursors. N,N-
Disubstituted imidazolinium and benzimidazolium bro-
mides 2 and 3 were prepared simply by heating the 2,4,6-
3
4
ladium. With their phosphine mimic ligating, NHC have
5
attracted the attention of several research groups. Various
tris(bromomethyl)mesitylene with 1-substituted imidazo-
NHC ligands have been synthesized within a short period
of time, and some of them have been successfully used for
10,11
lines or benzimidazoles (Scheme 1).
It has been found
that the in situ formation of the ligand by deprotonation of
the bis(imidazolinium) bromides lead to significantly bet-
6
a variety of palladium-catalyzed transformations. Al-
though NHC–palladium complexes used for Heck reac-
tion were claimed to be air and moisture stable, only a few
examples carried out under air were reported by Crabtree
15
ter results than use of the preformed carbene.
16
The Heck reaction has been shown to be very useful for
the preparation of disubstituted olefins in particular. The
rate of the coupling is dependent on a variety of para-
meters such as temperature, solvent, base and catalyst
loading. Generally, Heck reactions conducted with ter-
7
and co-workers. Most reactions catalyzed by NHC–pal-
ladium complexes are conducted under an inert atmo-
sphere. Therefore, easy-to-handle and highly efficient
catalysts that are stable towards oxidants and moisture
variations are still targets of pursuit. The use of water as a
solvent for chemical reactions clearly has both economi-
cal and environmental advantages because it is inexpen-
sive, abundant, nontoxic, nonflammable, and readily
1
7
18
tiary phosphine or NHC complexes required high tem-
peratures (higher than 120 °C) and polar solvents. For the
choice of base, we surveyed Cs CO , K CO , t-BuOK,
2
3
2
3
and K PO . Finally, we found that use of 1% mol
3
4
Pd(OAc) , 0.7% mol 2 or 3, 2 equivalents Cs CO or
8
2
2
3
separable from organic compounds. There have been a
t-BuOK, in DMF–H O (1:1) at 50 °C led to the best con-
2
version within 5 hours. We initially tested the catalytic
SYNLETT 2007, No. 6, pp 0889–0892
Advanced online publication: 26.03.2007
DOI: 10.1055/s-2007-973860; Art ID: S08406ST
0
3.
0
4.
2
0
0
7
activity of Pd(OAc) /2a–c for the coupling of p-bromo-
2
acetophenone with styrene (Table 1, entries 1–3).
©
Georg Thieme Verlag Stuttgart · New York

8
90
I. Özdemir et al.
LETTER
R
N
+
N
R
N
N
R
+
N
3 Br–
N
N
+
N
R
Br
Br
2
a
R = CH2C6H2(Me)3-2,4,6
R = CH2CH2OMe
2
b
2c
R = CH2CH2OEt
Br
R
R
1
N
+
N
N
N
N
R
N
+
3
Br–
N
+
N
R
3a
R = CH2C6H2(Me)3-2,4,6
3
b
c
R = CH2C6H2(OMe)3-3,4,5
R = CH2CH2OEt
3
Scheme 1 The synthesis of tris(azolinium) salts
In addition, the reactions were performed in air and with- dle, robust, and high-yielding procedure for Heck cou-
out degassing the water and DMF prior to use.
plings. The procedure is simple and efficient towards
various aryl bromides and does not require an induction
period. The advantage of the catalyst is the low loading
capabilities and it is use in air. The ligands are also easily
accessible. Further study is underway to optimize the re-
activity of these N-heterocyclic carbene precursors for C–
Control experiment indicated that the coupling reaction
did not occur in the absence of 2a. Under the determined
reaction conditions, a wide range of aryl bromides bearing
electron-donating or electron-withdrawing groups can re-
act with styrene affording the coupled products in excel-
lent yields. As expected, electron-deficient bromides were
beneficial for the conversions.
C and C–N coupling with Pd(OAc) , and transition-metal
2
complexes of Ru, Pd, and Rh to explore their catalytic ac-
tivity.
Under those conditions, p-bromoacetophenone, p-bro-
mobenzaldehyde, p-bromoanisole, and p-bromotoluene
react very cleanly with styrene in goods yields (Table 1,
entries 1, 2, 4, 10, 11, 16 and 19). The higher performance
Acknowledgment
This work was financially supported by the Technological and Sci-
of the tridentateazolium salts 2 and 3 are thought to be due entific Research Council of Turkey TÜBITAK [TÜBITAK TBAG-
to its better electron-donating ability and more steric hin- 2474 (104T085)] and Inönü University Research Fund (B.A.P.:
2
005/42 and 2004/Güz 8).
drance.
These results indicated that the catalytic system generated
in situ from tridentateazolinium salts and Pd(OAc) have References and Notes
2
an activity, which is superior or comparable to the mono-
(
1) (a) Heck, R. F. Palladium Reagents in Organic Synthesis;
1
9
dentate imidazolinium/Pd(OAc)2 system. However,
chloroarenes basically do not react under standard condi-
tions, and yields are lower than 4%.
Academic Press: London, 1985. (b) de Meijere, A.; Meier,
F. Angew. Chem., Int. Ed. Engl. 1994, 33, 2379. (c) Bräse,
S.; de Meijere, A. In Metal-Catalyzed Cross-Coupling
Reactions; Diederich, F.; Stang, P. J., Eds.; Wiley-VCH:
Weinheim, 1998, 99. (d) Beletskaya, I. P.; Cheprakov, A. V.
Chem. Rev. 2000, 100, 3009.
In conclusion, the tridentate carbene-ligand–palladium-
catalyst system disclosed herein represents an easy to han-
Synlett 2007, No. 6, 889–892 © Thieme Stuttgart · New York

LETTER
Heck Reaction of Aryl Bromides
891
Table 1 Heck Coupling Reaction of Aryl Bromides with Styrene
(3) (a) Böhm, V. P. W.; Herrmann, W. A. Chem. Eur. J. 2000,
, 1017. (b) Dupont, J.; Pfeffer, M.; Spencer, J. Eur. J.
6
Inorg. Chem. 2001, 1917. (c) Herrmann, W. A. Angew.
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Milstein, D. Chem. Rev. 2003, 103, 1759. (e)Bedford, R. B.
Chem. Commun. 2003, 1787. (f) Beletskaya, I. P.;
+
Br
R
Pd(OAc)2, 2 or 3, t-BuOK
Cheprakov, A. V. J. Organomet. Chem. 2004, 689, 4055.
DMF–H2O, 50 °C, 5 h
R
(
g) Christmann, U.; Vilar, R. Angew. Chem. Int. Ed. 2005,
4, 366.
(4) Yang, C.; Nolan, S. P. Synlett 2001, 1539.
4
Entry
Catalyst
2a
2b
2c
R
Yield (%)a
97
(
5) (a) Bourissou, D.; Guerret, O.; Gabbai, F. P.; Bertrand, G.
Chem. Rev. 2000, 100, 39. (b) Herrmann, W. A.; Köcher, C.
Angew. Chem., Int. Ed. Engl. 1997, 36, 2162.
1
2
3
4
5
6
7
8
9
COMe
COMe
COMe
COMe
COMe
COMe
CHO
CHO
CHO
CHO
CHO
CHO
OMe
OMe
OMe
OMe
OMe
OMe
Me
97
(
6) (a) Zhang, T. Y.; Zhang, H. Tetrahedron Lett. 2002, 43,
1
3
93. (b) Lee, S.; Hartwig, J. F. J. Org. Chem. 2001, 66,
402. (c) Cheng, J.; Trudell, M. L. Org. Lett. 2001, 3, 1371.
91
3a
3b
3c
93
(d) Fürstner, A.; Leitner, A. Synlett 2001, 290. (e) Titcomb,
L. R.; Caddick, S.; Cloke, F. G. N.; Wilson, D. J.;
88
McKerrecher, D. Chem. Commun. 2001, 1388. (f) Stauffer,
S. R.; Lee, S.; Stambuli, J. P.; Hauck, S. I.; Hartwig, J. F.
Org. Lett. 2000, 2, 1423. (g) Yang, C.; Lee, H. M.; Nolan, S.
P. Org. Lett. 2001, 3, 1511. (h) McGuinness, D. S.; Cavell,
K. J.; Skelton, B. W.; White, A. H. Organometallics 1999,
18, 1596. (i) McGuinness, D. S.; Green, M. J.; Cavell, K. J.;
Skelton, B. W.; White, A. H. J. Organomet. Chem. 1998,
86
2a
2b
2c
94
92
91
565, 165.
(
(
7) Peris, E.; Loch, J. A.; Mata, J.; Crabtree, R. H. Chem.
Commun. 2001, 201.
8) Li, C. J.; Chan, T. H. Organic Reactions in Aqueous Media;
Wiley: New York, 1997.
1
1
1
1
1
1
1
1
1
1
2
2
2
2
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
3a
3b
3c
96
96
90
(9) (a) Genet, J.-P.; Savignac, M. J. Organomet. Chem. 1999,
76, 305. (b) Sakurai, H.; Sukuda, T.; Hirao, T. J. Org.
5
2a
2b
2c
87
Chem. 2002, 67, 2721. (c) Parisot, S.; Kolodziuk, R.; Henry,
C. G.; Iourtchenko, A.; Sinou, D. Tetrahedron Lett. 2002,
84
43, 7397. (d) Botella, L.; Najera, C. Angew. Chem. Int. Ed.
2002, 41, 179. (e) Schönfelder, D.; Nuyken, O.;
79
Weberskirch, R. J. Organomet. Chem. 2005, 690, 4648.
(10) (a) Özdemir, I.; Demir, S.; Yaşar, S.; Çetinkaya, B. Appl.
Organomet. Chem. 2005, 19, 55. (b) Özdemir, I.; Demir, S.;
Çetinkaya, B. Tetrahedron 2005, 61, 9791. (c) Özdemir, I.;
Gürbüz, N.; Gök, Y.; Çetinkaya, E.; Çetinkaya, B. Synlett
3a
3b
3c
89
85
81
2005, 2394.
(
11) (a) Özdemir, I.; Gök, Y.; Gürbüz, N.; Yaşar, S.; Çetinkaya,
E.; Çetinkaya, B. Polish J. Chem. 2004, 78, 2141.
2a
2b
2c
84
(
b) Özdemir, I.; Gök, Y.; Gürbüz, N.; Çetinkaya, E.;
Me
81
Çetinkaya, B. Synth. Commun. 2004, 34, 4135.
(c) Özdemir, I.; Gök, Y.; Gürbüz, N.; Çetinkaya, E.;
Çetinkaya, B. Heteroat. Chem. 2004, 15, 419.
12) Özdemir, I.; Gürbüz, N.; Seçkin, T.; Çetinkaya, B. Appl.
Organomet. Chem. 2005, 19, 633.
Me
79
3a
3b
3c
Me
83
(
(
Me
81
13) General Procedure for the Synthesis of
Tridentateazolinium Bromides
2
Me
78
To a solution of 1-alkylimidazoline or 1-alkylbenzimidazole
(15 mmol) in DMF (15 mL) was added slowly 2,4,6-
tris(bromomethyl)mesitylene (5 mmol) at 25 °C and the
a
Reaction conditions: p-BrC H R (1.0 mmol), styrene (1.5 mmol), t-
BuOK (2 mmol), Pd(OAc) (1.0%), 2 or 3 (0.7 mmol%), H O–DMF
6 ml, 1:1), 50 °C, 5 h. Purity of compounds was checked by NMR
6
4
2
2
(
resulting mixture was heated for 5 h at 60 °C. Then, Et O (15
2
and yields are based on aryl bromide.
mL) was added to obtain a white crystalline solid, which was
filtered off. The solid was washed with Et O (3 × 15 mL),
2
dried under vacuum. The crude product was crystallized
from EtOH–Et O (2:1).
(
2) (a) Blaser, H.-U.; Indolese, A.; Schnyder, A.; Steiner, H.;
Studer, M. J. Mol. Catal. A: Chem. 2001, 173, 3. (b) de
Vries, J. G.; de Vries, A. H. M. Eur. J. Org. Chem. 2003,
2
2,4,6-Tris[3-(2,4,6-trimethylbenzyl)imidazolinium]methyl-
mesitylene bromide (2a): yield 4.67 g (93%); mp 86–
–
1 1
2
87 °C. IR: n(CN) = 1650 cm . H NMR (CDCl ): d = 2.16
799. (c) Blaser, H.-U.; Indolese, A.; Naud, F.; Nettekoven,
3
and 2.22 [s, 27 H, CH C H (CH ) -2,4,6], 2.49 [s, 9 H,
U.; Schnyder, A. Adv. Synth. Catal. 2004, 346, 1583.
2
6
2
3 3
C (CH ) (CH ) -2,4,6], 3.64 and 4.29 [t, J = 10.8, 10.4 Hz,
6
3 3
2 3
1
2 H, NCH CH N], 4.69 [s, 6 H, C (CH ) (CH ) -2,4,6],
2 2 6 3 3 2 3
4
.91 [s, 6 H, CH C H (CH ) -2,4,6], 6.76 [s, 6 H,
2
6
2
3 3
Synlett 2007, No. 6, 889–892 © Thieme Stuttgart · New York

8
92
I. Özdemir et al.
CH C H (CH ) -2,4,6], 9.54 (s, 3 H, NCHN). C{ H}NMR
LETTER
3,4,5], 57.1 and 61.2 [CH C H (OCH ) -3,4,5], 106.5,
1
3
1
2
6
2
3 3
2
6
2
3 3
(
[
CDCl ): d = 20.6 and 21.3 [CH C H (CH ) -2,4,6], 18.0
138.6, 141.5 and 153.9 [CH C H (OCH ) -3,4,5], 129.2,
142.4 and 142.7 [C (CH ) (CH ) -2,4,6], 114.2, 114.7,
6 3 3 2 3
3
2
6
2
3
3
2 6 2 3 3
C (CH ) (CH ) -2,4,6], 46.5 [C (CH ) (CH ) -2,4,6], 47.9
6
3 3
2
3
6
3
3
2 3
and 48.0 (NCH CH N), 50.3 [CH C H (CH ) -2,4,6], 126.0,
127.5, 127.8, 132.0 and 132.1 (NC H N), 190.1 (NCHN).
2
2
2
6
2
3 3
6 4
1
30.1, 138.2 and 139.0 [CH C H (CH ) -2,4,6], 129.4,
Anal. Calcd for C H N O Br : C, 58.48; H, 5.37; N, 6.49.
63 69 6 9 3
2
6
2
3 3
1
41.4 and 156.8 [C (CH ) (CH ) -2,4,6], 162.9 (NCHN).
Found: C, 58.45; H, 5.36; N, 6.50.
6
3 3
2 3
Anal. Calcd for C H N Br : C, 60.90; H, 6.91; N, 8.36.
2,4,6-Tris[3-(ethoxtethyl)benzimidazolium]methyl-
mesitylene bromide (3c): yield 4.01 g (83%); mp 282–
5
1
69
6
3
Found: C, 60.92; H, 6.88; N, 8.35.
,4,6-Tris[3-(methoxyethyl)imidazolinium]methyl-
mesitylene bromide (2b): yield 3.16 g (81%); mp 156–
–
1 1
2
283 °C. IR n(CN) = 1563 cm . H NMR (CDCl ): d = 0.79 (t,
3
J = 6.8 Hz, 9 H, NCH CH OCH CH ), 2.48 [s, 9 H, C
2
2
2
3
6
–
1 1
1
9
3
57 °C. IR: n(CN) = 1660 cm . H NMR (CDCl ): d = 2.44 [s,
(CH ) (CH ) -2,4,6], 3.76 (quart, J = 7.2 Hz, 6 H,
3 3 2 3
3
H, C (CH ) (CH ) -2,4,6], 3.28 (s, 9 H, NCH CH OCH ),
.41 and 3.52 (t, J = 4.8 Hz, 12 H, NCH CH N), 4.14 (t,
NCH CH OCH CH ), 3.79 (t, J = 12.0 Hz, 6 H,
6
3 3
2 3
2
2
3
2 2 2 3
NCH CH OCH CH ), 4.85 (t, J = 12.0 Hz, 6 H,
2 2 2 3
2
2
J = 11.0 Hz, 6 H, NCH CH OCH ), 4.38 (t, J = 11.2 Hz, 6 H,
NCH CH OCH CH ), 5.90 [s, 6 H, C (CH ) (CH ) -2,4,6],
2
2
3
2 2 2 3 6 3 3 2 3
NCH CH OCH ), 4.65 [s, 6 H, C (CH ) (CH ) -2,4,6], 9.14
8.12 (d, J = 7.6 Hz, 3 H, NC H N), 8.29 (d, J = 8.0 Hz, 3 H,
6 4
2
2
3
6
3
3
2 3
1
3
1
(
[
(
(
s, 3 H, NCHN). C{ H}NMR (CDCl ): d = 17.7
NC H N), 7.76 (m, 6 H, NC H N), 10.09 (s, 3 H, NCHN).
3
6 4 6 4
1
3
1
C (CH ) (CH ) -2,4,6], 59.0 (NCH CH OCH ), 47.7
C{ H}NMR (CDCl ): d = 17.1 [C (CH ) (CH ) -2,4,6],
3 6 3 3 2 3
6
3 3
2
3
2
2
3
NCH CH OCH ), 47.9 (NCH CH OCH ), 50.1 and 50.6
15.4 (NCH CH OCH CH ), 46.7 (NCH CH OCH CH ),
2
2
3
2
2
3
2 2 2 3 2 2 2 3
NCH CH N), 69.9 [C (CH ) (CH ) -2,4,6], 129.1, 141.0
47.3 (NCH CH OCH CH ), 66.2 (NCH CH OCH CH ),
2 2 2 3 2 2 2 3
2
2
6
3 3
2
3
and 157.1 [C (CH ) (CH ) -2,4,6], 162.6 (NCHN). Anal.
68.2 [C (CH ) (CH ) -2,4,6], 129.4, 142.0 and 142.8
6
3 3
2 3
6 3 3 2 3
Calcd for C H N O Br : C, 45.99; H, 6.56; N, 10.73.
[C (CH ) (CH ) -2,4,6], 114.8, 114.9, 127.4, 127.6, 131.8
6 3 3 2 3
3
0
51
6
3
3
Found: C, 46.00; H, 6.55; N, 10.75.
,4,6-Tris[3-(ethoxyethyl)imidazolinium]methylmesitylene
bromide (2c): yield 3.54 g (86%); mp 123–124 °C. IR:
and 132.4 (NC H N), 171.2 (NCHN). Anal. Calcd for
C H N O Br : C, 55.74; H, 5.92; N, 8.67. Found: C, 55.75;
45 57 6 3 3
H, 5.90; N: 8.66.
General Procedure for the Heck Coupling Reaction
6 4
2
–
1 1
n
= 1659 cm . H NMR (CDCl ): d = 0.96 [t, J = 6.9 Hz,
(
CN)
3
9
2
H, NCH CH OCH CH ], 2.31 [s, 9 H, C (CH ) (CH ) -
Pd(OAc) (1.0 mmol%), 2,4,6-tris[(3-alkyl)azo-
2
2
2
3
6
3 3
2
3
2
,4,6], 3.30 (q, J = 6.9 Hz, 6 H, NCH CH OCH CH ), 3.42
linium]methylmesitylene bromide 2 or 3 (0.7 mmol%), aryl
bromide (1.0 mmol), styrene (1.5 mmol), t-BuOK (2 mmol),
2
2
2
3
and 3.68 (m, 12 H, NCH CH N), 4.06 (t, J = 10.4 Hz, 6 H,
2
2
NCH CH OCH CH ), 4.25 (t, J = 10.6 Hz, 6 H,
H O–DMF (6 mL, 1:1) were added to a small Schlenk tube
2
2
2
3
2
NCH CH OCH CH ), 4.50 [s, 6 H, C (CH ) (CH ) -2,4,6],
and the mixture was heated at 50 °C for 5 h. Finally, the
mixture was cooled, extracted with EtOAc–hexane (1:5),
filtered through a pad of silica gel with copious washings,
concentrated and purified by flash chromatography on silica
gel. Purity of the compounds was checked by NMR and GC,
yields are based on aryl bromide.
2
2
2
3
6
3 3
2 3
1
3
1
9
.03 (s, 3 H, NCHN). C{ H}NMR (CDCl ): d = 17.5
6 3 3 2 3 2 2 2 3
3
[
(
(
[
[
C (CH ) (CH ) -2,4,6], 15.5 (NCH CH OCH CH ), 66.7
NCH CH OCH CH ), 47.9 (NCH CH OCH CH ), 48.4
NCH CH OCH CH ), 50.5 and 50.8 (NCH CH N), 68.3
C (CH ) (CH ) -2,4,6], 129.2, 141.2 and 157.2
2
2
2
3
2
2
2
3
2
2
2
3
2
2
6
3 3
2 3
C (CH ) (CH ) -2,4,6], 162.7 [NCHN]. Anal. Calcd for
(14) (a) Çetinkaya, B.; Özdemir, I.; Bruneau, C.; Dixneuf, P. H.
Eur. J. Inorg. Chem. 2000, 29. (b) Çetinkaya, B.;
Çetinkaya, E.; Hitchcock, P. B.; Lappert, M. F.; Özdemir, I.
J. Chem. Soc., Dalton Trans. 1997, 1359. (c) Çetinkaya, B.;
Özdemir, I.; Demir, S. J. Mol. Catal. A: Chem. 2004, 208,
109. (d) Özdemir, I.Şahin, N.; Gök, Y.; Demir, S.;
Çetinkaya, B. J. Mol. Catal. A: Chem. 2005, 234, 181.
(15) (a) Semeril, D.; Bruneau, C.; Dixneuf, P. H. Adv. Synth.
Catal. 2002, 344, 585. (b) Semeril, D.; Cleran, M. D.;
Bruneau, C.; Dixneuf, P. H. Adv. Synth. Catal. 2001, 343,
184. (c) Castarlenes, R.; Alaoui-Abdallaoui, I.; Semeril, D.;
Mernari, B.; Guesmi, S.; Dixneuf, P. H. New J. Chem. 2003,
27, 6. (d) Hillier, A. C.; Grasa, G. A.; Viciu, M. S.; Lee, H.
M.; Yang, C.; Nolan, S. P. J. Organomet. Chem. 2002, 653,
69. (e) Zhang, C.; Trudell, M. L. Tetrahedron Lett. 2000, 41,
595.
6
3 3
2 3
C H N O Br C, 48.01; H, 6.96; N, 10.18. Found: C,
33
57
6
3
3:
48.03; H, 6.99; N: 10.15.
2,4,6-Tris[3-(2,4,6-trimethylbenzyl)benzimida-
zolium]methylmesitylene bromide (3a): yield 5.00 g (87%);
–
1 1
mp 214–215 °C. IR: n(CN) = 1562 cm . H NMR (DMSO-
d ): d = 2.22 and 2.24 [s, 27 H, CH C H (CH ) -2,4,6], 2.39
6
2
6
2
3 3
[
s, 9 H, C (CH ) (CH ) -2,4,6], 5.94 and 5.95 [s, 12 H,
6 3 3 2 3
C (CH ) (CH ) -2,4,6 and CH C H (CH ) -2,4,6 ], 6.93 [s, 6
6
3 3
2
3
2
6
2
3 3
H, CH C H (CH ) -2,4,6], 7.16 [d, J = 8.0 Hz, 3 H,
2
6
2
3 3
NC H N], 7.56 and 7.67 (t, J = 7.6 Hz, 6 H, NC H N), 8.13
6
4
6
4
(
d, J = 8.4 Hz, 3 H, NC H N), 10.33 (s, 3 H, NCHN).
6 4
13
1
C{ H}NMR (DMSO-d ): d = 20.4 and 21.3
6
[CH C H (CH ) -2,4,6], 17.2 [C (CH ) (CH ) -2,4,6], 47.1
2 6 2 3 3 6 3 3 2 3
[
C (CH ) (CH ) -2,4,6], 47.4 [CH C H (CH ) -2,4,6],
6 3 3 2 3 2 6 2 3 3
1
1
1
26.8, 130.4, 138.6 and 139.1 [CH C H (CH ) -2,4,6],
2 6 2 3 3
29.5, 141.9 and 142.9 [C (CH ) (CH ) -2,4,6], 114.3,
(16) Farina, V. Adv. Synth. Catal. 2004, 346, 1553.
(17) Littke, A. F.; Fu, G. C. Angew. Chem. Int. Ed. 2002, 41,
4176.
6
3 3
2 3
15.2, 127.3, 127.8, 132.1 and 132.4 (NC H N), 163.1
6
4
(
NCHN). Anal. Calcd for C H N Br : C, 65.80; H, 6.05; N,
63 69 6 3
7
.31. Found: C, 65.83; H, 6.02; N, 7.30.
(18) (a) Loch, J. A.; Albrecht, M.; Peris, E.; Mata, J.; Faller, J.
W.; Crabtree, R. H. Organometallics 2002, 21, 700.
(b) Peris, E.; Crabtree, R. H. Coord. Chem. Rev. 2004, 248,
2239.
(19) (a) Gürbüz, N.; Özdemir, I.; Demir, S.; Çetinkaya, B. J. Mol.
Catal. A: Chem. 2004, 209, 23. (b) Özdemir, I.; Çetinkaya,
B.; Demir, S.; Gürbüz, N. Catal. Lett. 2004, 97, 37.
(c) Özdemir, I.; Demir, S.; Yaşar, S.; Çetinkaya, B. Appl.
Organomet. Chem. 2005, 19, 55. (d) Gürbüz, N.; Özdemir,
I.; Seçkin, T.; Çetinkaya, B. J. Inorg. Organomet. Polym.
2004, 14, 149.
2,4,6-Tris[3-(3,4,5-trimethoxybenzyl)benzimida-
zolium]methylmesitylene bromide (3b): yield 5.81 g (90%);
–
1 1
mp 195–196 °C. IR n(CN) = 1596 cm . H NMR (CDCl ):
3
d = 2.44 [s, 9 H, C (CH ) (CH ) -2,4,6], 3.72 and 3.77 [s, 27
6
3 3
2 3
H, CH C H (OCH ) -3,4,5], 5.84 [s, 6 H, C (CH ) (CH ) -
2
6
2
3
3
6
3
3
2 3
2,4,6], 5.90 [s, 6 H, CH C H (OCH ) -3,4,5], 6.82 [s, 6 H,
2 6 2 3 3
CH C H (OCH ) -3,4,5], 7.56 (m, 9 H, NC H N), 8.25 (d,
2
6
2
3 3
6
4
J = 8.1 Hz, 3 H, NC H N), 10.59 (s, 3 H, NCHN).
6
4
13
1
C{ H}NMR (CDCl ): d = 18.5 [C (CH ) (CH ) -2,4,6],
3
6
3
3
2 3
47.5 [C (CH ) CH ) -2,4,6], 52.7 [CH C H (OCH ) -
6 3 3 ( 2 3 2 6 2 3 3
Synlett 2007, No. 6, 889–892 © Thieme Stuttgart · New York

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