Synthesis of Pd(II) 1-alkylperimidine complexes as efficient catalysts for Suzuki reactions involving arylchlorides

Article abstract of DOI:10.1007/s11173-005-0011-8

Three palladium(II) complexes of the type [PdCl₂(PPh ₃)L] (L-1-alkylperimidine) have been prepared by reactions of [PdCl₂(PR₃)]₂ with 1-alkylperimidine. The complexes were characterized by conventiona

Full text of DOI:10.1007/s11173-005-0011-8

Russian Journal of Coordination Chemistry, Vol. 31, No. 2, 2005, pp. 142–145. From Koordinatsionnaya Khimiya, Vol. 31, No. 2, 2005, pp. 153–156.
Original English Text Copyright © 2005 by Özdemir, Alıcı, Gürbüz, B. Çetinkaya, E. Çetinkaya.
Synthesis of Pd(II) 1-Alkylperimidine Complexes as Efficient
Catalysts for Suzuki Reactions Involving Arylchlorides1
÷
I. Özdemir*, B. Alıcı*, N. Gürbüz*, B. Çetinkaya**, and E. Çetinkaya**
* Inönü University, Faculty of Science and Letters, Chemistry Department, 44069 Malatya, Turkey
e-mail: iozdemir@inonu.edu.tr
÷
** Ege University, Department of Chemistry, 35100 Bornova-Izmı÷r, Turkey
Received February 3, 2004
Abstract—Three palladium(II) complexes of the type [PdCl2(PPh3)L] (L—1-alkylperimidine) have been pre-
pared by reactions of [PdCl2(PR3)]2 with 1-alkylperimidine. The complexes were characterized by conventional
spectroscopic methods and elemental analyses. The incorporation of N-coordinated perimidine complexes of
palladium(II) gave high catalytic activity in the Suzuki coupling deactivated aryl chloride substrates.
Interaction of aryl halides with arylboronic acids
(via Suzuki reaction) representing one of the most gen-
eral C–C coupling reactions in organic synthesis, is cat-
alyzed by palladium complexes in homogeneous solu-
tion according to the following equation [1–3]:
Our contribution to this field has started with syn-
theses of 2-imidazoline and benzimidazole complexes
of Pt(II), Rh(I), Ru(II), and Pd(II) which are capable of
catalyzing the cyclopropanation of styrene with ethyl
diazoacetate and intramolecular cyclization of (Z)-3-
methylpent-2-en-4-yn-1-ol into 2,3-dimethylfuran in
good yields [18–22]. Recently, we have developed
improved procedures of Heck and Suzuki reactions
of aryl chlorides making use of novel ligands
1,3-bis(2,4,6-trimethylbenzyl)imidazolium chloride,
1-alkylimidazoline, α-bis(imine) [23, 24]. The 1-alkyl-
perimidine complexes are insensitive to air and mois-
ture and are thermally stable in both the solid state and
in solution.
However, the development of new ligands or the
application of existing ligands in Suzuki reaction, par-
ticularly those involving aryl chlorides as substrates, is
still of considerable importance.
We report here the straightforward preparation of a
series phosphine palladium complexes with N-coordi-
nated 1-alkylperimidine derivatives. These complexes
were shown to be effective catalysts for Suzuki reaction
especially with arylchlorides.
[Cat.]
X + ArB(OH)2
Ar + XB(OH)2,
Base
(1)
R
R
X = Cl, Br, I.
The reactivity of the aryl halide component
decreases drastically in the X order I > Br > Cl and elec-
tron-withdrawing substituents R are required for the
chlorides to react [1–6]. The low reactivity of aryl chlo-
rides in cross-coupling reactions is generally ascribed
to their reluctance to oxidatively add to Pd(0) [4–6].
Current interest focuses on the use of aryl chlorides
since they are cheaper and more readily accessible than
bromides and iodides [7]. Significant advances have
been recently achieved by use of palladacycles and
especially, by use of bulky and electron-rich tertiary
phosphines as catalyst modifiers systems [8–14]. How-
ever, the major drawback of these is that the phosphine
ligands are comparatively difficult to make or rather
expensive. Furthermore, tertiary phosphines require air-
free handling to prevent their oxidation and are suscepti-
ble to P–C bond cleavage at elevated temperatures [15].
EXPERIMENTAL
All reactions were performed using Schlenk-type
flask under argon and standard high vacuum-line tech-
niques. Solvents were analytical grade and distilled
under argon from sodium benzophenone (Et2O, diox-
ane, toluene, n-hexane). 1-Substituted perimidine (A)
were prepared according to the literature [25, 26].
NMR spectra were recorded at 297 K on a Bruker
AC300P FT spectrometer operating at 300.13 MHz
(1H), 75.47 MHz (13C). FT-IR spectra were recorded on
a Mattson 1000 spectrophotometer. Samples were pre-
pared as KBr discs. Elemental analyses were performed
by TUBITAK Microlab (Ankara).
On the other hand, transition metal complexes with
ligands containing nitrogen-donor atoms have been
shown their potential to successfully promote the cata-
lytic transformation of organic compounds [16, 17].
These discoveries motivate the search for the new metal
complexes with N-coordinated ligands and the evalua-
tion of their catalytic properties.
1
This article was submitted by the authors in English.
1070-3284/05/3102-0142 © 2005 Pleiades Publishing, Inc.

SYNTHESIS OF Pd(II) 1-ALKYLPERIMIDINE COMPLEXES
143
Preparation of 1-(2-Methoxyethyl)perimidinedi-
chloro(triphenylphosphine) Palladium(II) (Ia).
1H NMR (CDCl3, 293 K) δ, ppm: 8.11 (s., 1H, C(2)–
H), 7.43–7.22 (m., 9H, Ar–H), 6.12 (d., J = 7.0 Hz, 2H,
Ar2–H), 5.28 (s., 2H, CH2C6H5) 7.49 (m., 15H,
P(C6H5)3).
13C{H} NMR (CDCl3) δ, ppm: 153.5 (2-CH), 142.4,
138.9, 137.1, 133.7, 131.8, 128.5, 128.3, 126.8, 124.2,
121.7, 117.3, 111.5, 101.4 (Carene), 55.3 (NCH2C6H5),
130.8, 131.5, 132.1, and 139.4 (P(C6H5)3).
A solution of 1-(2-methoxyethyl)perimidine (113 mg,
0.5 mmol) in toluene (15 ml) and [PdCl2(PPh3)]2
(220 mg, 0.25 mmol) was heated for 2 h under reflux.
n-Hexane (5 ml) was added to the warm solution. Upon
cooling to room temperature, pale yellow crystals of com-
plex Ia were filtered off, washed with hexane (2 × 5 ml)
and dried in vacuum. Yield 0.26 g (79%), m.p. = 267–
268°C; FT-IR ν(CN) 1653 cm–1.
Preparation of 1-(2-Phenylethyl)perimidine
dichloro(trilphenylphosphine) Palladium(II) (Ic).
Compound Ic was prepared in the same way as Ia from
1-(ethyphenyl)perimidine (136 mg, 0.5 mmol) and
[PdCl2(PPh3)]2 (220 mg, 0.25 mmol) to give pale yellow
crystals of Ic. Yield 306 mg (86%), m.p. = 245–246°C;
ν(CN) 1651 cm–1.
For C32H29N2OPPdCl2
anal. calcd, %: C, 57.71;
Found, %: C, 57.78;
H, 4.36;
H, 4.23;
N, 4.21.
N, 4.25.
1H NMR (CDCl3, 293 K) δ, ppm: 8.03 (s., 1H, C(2)–
H), 7.41–7.20 (m., 4H, Ar–H), 6.13 (d., J = 7.0 Hz, 2H,
Ar2–H), 3.69 (t., J = 4.2 Hz, 2H, NCH2CH2OCH3),
3.45 (t., J = 4.2 Hz, 2H, NCH2CH2OCH3), 3.35 (s., 3H,
NCH2CH2OCH3), 7.49 (m., 15H, P(C6H5)3).
For C37H31N2PPdCl2
anal. calcd, %: C, 62.41;
Found, %: C, 62.66;
H, 4.36;
H, 4.38;
N, 3.94.
N, 3.99.
13C NMR (CDCl3, 293 K): δ, ppm: 157.1 (2-CH),
141.6, 137.9, 137.0, 131.7, 127.5, 126.8, 123.4, 123.2,
114.5, 108.7 (Carene), 59.6 (NCH2CH2OCH3), 56.8
(NCH2CH2OCH3), 71.5 (NCH2CH2OCH3), 130.0,
131.3, 131.9 and 139.8 (P(C6H5)3).
1H NMR (CDCl3, 293 K) δ, ppm: 7.95 (s., 1H, C(2)–
H), 6.86–7.27 (m., 9H, Ar–H), 6.10 (d., J = 7.0 Hz, 2H,
Ar2–H), 4.51 (s., 4H, CH2CH2C6H5) 7.49 (m., 15H,
P(C6H5)3).
Preparation
of
1-Benzylperimidinedichlo-
13C{H}NMR (CDCl3) δ, ppm: 152.9 (2-CH), 141.8,
ro(triphenylphosphine) Palladium(II) (Ib).
138.6, 138.1, 134.0, 131.5, 127.7, 127.3, 126.6, 122.8,
Compound Ib was prepared in the same way as Ia
from 1-benzylperimidine (129 mg, 0.5 mmol) and
[PdCl2(PPh3)]2 (220mg, 0.25 mmol) to give yellow
crystals of Ib. Yield 293 mg (84%), m.p. = 241–242°C;
ν(CN) 1629 cm–1.
121.5,
118.4,
110.7,
102.6 (Carene), 54.8
(NCH2CH2C6H5), 31.7 (NCH2CH2C6H5), 131.4, 131.9,
132.6, and 138.9 (P(C6H5)3).
RESULTS AND DISCUSSION
For C36H29N2PPdCl2
anal. calcd, %: C, 61.94;
Found, %: C, 62.01;
H, 4.16;
H, 4.19;
N, 4.02.
N, 4.10.
The N-coordinated palladium complexes were syn-
thesized according to the following equation:
Cl
R'
N
Ph3P Pd
N
N R'
Toluene
Cl
+ [PdCl2(PPh3)]2
110°C
N
(2)
Ia: R = CH2CH2OCH3,
Ib: R = CH2C6H5,
Ic: R = CH2CH2C6H5.
The reaction of the 1-alkylperimidine with binuclear (Table 1). 13C NMR spectroscopy was the most useful
[PdCl2(PPh3)]2 proceeds smoothly, in refluxing toluene, tool for structure elucidation.
to give the pale yellow complexes Ia (79%), Ib (84%),
Ic (86%). Complexes Ia–Ic, which are very stable in
the solid state, have been characterized by analytical
and spectroscopic data. The spectroscopic properties
indicated that they all are N(3)-bonded.
The nature of the bonding in the perimidine com- shifts were consistent with the proposed structure, the
plexes Ia–Ic was readily shown by NMR spectroscopy imino carbon resonance appeared as a typical singlet in
Thus, from our previous experience [27–29], we
expected that C-coordination would result in a shift of
the carbene carbon nucleus signal toward low field, i.e.,
190–212 ppm, while N-coordination would result in a
higher field shift towards 155 ppm. 13C NMR chemical
RUSSIAN JOURNAL OF COORDINATION CHEMISTRY Vol. 31 No. 2 2005

144
ÖZDEMIR et al.
Table 1. Selected analytical data for the new perimidine pal-
ladium complexes Ia–Ic
in the Suzuki type coupling of para-substituted aryl
halides with phenylboronic acid, classical conditions
for solvent and base were chosen (dioxane as solvent,
Cs2CO3 as base, and reaction temperature of 80°C).
The coupling of activated and deactivated aryl halo-
genides and phenylboronic acid proceeds in high yields
and quite rapidly even with a low catalyst loading. The
results were summarized in Table 2. Under those con-
ν(C=N)
Com- Yield M. p.
plex (%) (°C)
13C NMR 1H NMR
C(2) (δ, ppm) H(2) (δ, ppm)
(cm–1)
Ia
Ib
Ic
79 267–268 1653
84 241–242 1629
86 245–246 1651
157.1
153.5
152.9
8.03
8.11
7.95
ditions,
4-chloroacetophenone,
p-chloroanisole,
p-chlorotoluene, p-chlorobenzaldehyde and chloroben-
zene react very cleanly with phenylboronic acid in
good yields (Table 2, entry 1, 2, 4, 7, 10, and 13).
the 1H-decoupled mode at 157.1, 153.5, and 152.9 ppm,
respectively, for complexes Ia–Ic. The 1H NMR spectra
of the complexes further supported the assigned struc-
tures; the resonances for C(2)–H were observed as
sharp singlets at 8.03, 8.11, and 7.99 ppm, respectively,
for complexes Ia–Ic.
From readily available starting materials such as
1-alkylperimidine, three new N-coordinated palladium
complexes (Ia–Ic) have been prepared and character-
ized. Also we have found that the very easily synthe-
sized, comparatively inexpensive complexes Ia–Ic
show by far the highest activity yet reported in Suzuki
coupling of arylchlorides, regardless of whether the
substrates are electron rich or poor. The procedure is
simple and efficient towards various arylchlorides and
does not require induction periods. Investigations
focusing on the reactivity profile of I and related palla-
dium complexes, their efficiency as catalysts in cross-
The IR data for complexes Ia–Ic clearly indicate the
presence of the –C=N– group with the ν(C=N) vibration
at 1653, 1629, and 1651 cm–1, respectively, for com-
plexes Ia–Ic. The NMR and IR values are similar to
those found for N-coordinated metal complexes [18–24].
The palladium-catalyzed cross-coupling of arylbo-
ronic acids with aryl halides has been shown to proceed
under a variety of conditions: a wide range of bases and
solvents, as well as catalysts, have been employed with
varying degrees of success according to the substrates
[1, 2]. In a first test of the activity of complexes Ia–Ic coupling reactions are ongoing in our laboratories.
Table 2. The Suzuki coupling reaction of arylchlorides with phenylboronic acid*
Cat. (1.5 mol %)
R
+
B(OH)2
R
Cl
Cs2CO2 (1.5 equiv.),
80°C
Entry
R
Cat.
Ia
Yield (%)**
1
2
COCH3
COCH3
COCH3
OCH3
OCH3
OCH3
CH3
96
93
91
94
90
88
94
92
90
95
90
88
89
85
84
Ib
Ic
Ia
Ib
Ic
Ia
Ib
Ic
Ia
Ib
Ic
Ia
Ib
Ic
3
4
5
6
7
8
CH3
9
CH3
10
11
12
13
14
15
CHO
CHO
CHO
H
H
H
* Reaction conditions: 1.0 mmol of p-R-C H X, 1.5 mmol of phenylboronic acid, 1.5 mmol Cs CO , 1.5 mol % Pd catalyst, dioxane
6
4
2
3
(3 ml), 80°C, 2.5 h.
** Purity of yield checked by NMR, all reactions were monitored by TLC.
RUSSIAN JOURNAL OF COORDINATION CHEMISTRY Vol. 31 No. 2 2005

SYNTHESIS OF Pd(II) 1-ALKYLPERIMIDINE COMPLEXES
145
14. Littke, A.D., Dai, C., and Fu, G.C., J. Am. Chem. Soc.,
ACKNOWLEDGMENTS
2000, vol. 122, no. 17, p. 4020.
We are grateful to Technological and Scientific
15. Applied Homogeneous Catalysis with Organometallic
Compounds, Herrmann, W.A., Cornils, B, and Her-
rmann, W.A., Eds, Weinhem: VCH, 1996, p. 712.
16. Mizuroki, T., Mori, K., and Ozaki, A., Bull. Chem. Soc.
Jpn., 1971, vol. 44, no. 2, p. 581.
÷
Research Council of Turkey TÜBITAK TBAG-2474
(104T085) and Inönü University Research Fund (BAP
2002/19) for financial support of this work.
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