Palladium imine and amine complexes derived from 2-thiophenecarboxaldehyde as catalysts for the Suzuki cross-coupling of aryl bromides

Article abstract of DOI:10.1016/j.molcata.2006.04.009

A range of square-planar trans-dichloro palladium(II) complexes containing N-(2-thienylmethylene)-aniline and N-(2-thienylmethyl)-aniline derived ligands has been synthesized and characterized. The use of these complexes as catalysts for the Suzuki coupling of various aryl bromides and phenyl boronic acid has been examined.

Full text of DOI:10.1016/j.molcata.2006.04.009

Journal of Molecular Catalysis A: Chemical 257 (2006) 67–72
Palladium imine and amine complexes derived from
2-thiophenecarboxaldehyde as catalysts for the Suzuki
cross-coupling of aryl bromides
Julia Wiedermanna, Kurt Mereiterb, Karl Kirchnera,∗
a Institute of Applied Synthetic Chemistry, Vienna University of Technology, Getreidemarkt 9, A-1060 Vienna, Austria
b Institute of Chemical Technologies and Analytics, Vienna University of Technology, Getreidemarkt 9, A-1060 Vienna, Austria
Available online 11 May 2006
Abstract
A range of square-planar trans-dichloro palladium(II) complexes containing N-(2-thienylmethylene)-aniline and N-(2-thienylmethyl)-aniline
derived ligands has been synthesized and characterized. The use of these complexes as catalysts for the Suzuki coupling of various aryl bromides
and phenyl boronic acid has been examined.
© 2006 Elsevier B.V. All rights reserved.
Keywords: 2-Thiophenecarboxaldehyde; Imine ligands; Amine ligands; Suzuki cross-coupling; Palladium complexes
1. Introduction
2. Experimental
Palladium-catalyzed Suzuki cross-coupling reactions of aryl
halides with arylboronic acids have emerged as an extremely
efficient and thus important tool in organic synthesis [1].
Accordingly, in the past few years many efforts have been
made to develop new catalytic systems [2–6]. Among the
various palladium-catalyzed systems reported, complexes con-
taining sterically demanding chelating ␣-diimine (diazabuta-
diene) and ␤-diimine ligands have been found to be highly
efficient as catalysts for Suzuki cross-coupling reactions [7].
In contrast to these types of catalysts, palladium compounds
containing monodentate imine ligands have not been utilized
as catalysts for Suzuki coupling reactions. Here we wish
to report on the synthesis and characterization of a series
of palladium complexes containing N-(2-thienylmethylene)-
aniline and N-(2-thienylmethyl)-aniline derived ligands and
describe the use of these palladium complexes in the catalytic
cross-coupling of various aryl bromides with phenylboronic
acid.
2.1. General
All manipulations were performed under an inert atmo-
sphere of argon by using Schlenk techniques. The solvents were
purified according to standard procedures. The starting materi-
als 2-thiophenecarboxaldehyde and 2,4,6-trimethylaniline were
purchased from Aldrich and used without further purifica-
tion. 1-Propaneamine was purchased from Merck, S-(−)-
1-phenylethylamine was purchased from Fluka. The lig-
ands N-(2-thienylmethylene)-1-propaneamine (1b), S-(−)-N-
(2-thienylmethylene)-1-phenylethylamine (1c) [8], and N-(2-
thienylmethyl)-aniline (2) were prepared according to the lit-
erature [9].
The deuterated solvents were purchased from Aldrich and
dried over 4 A molecular sieves. H and 13C{ H} NMR spectra
1
1
˚
were recorded on a Bruker AVANCE-250 spectrometer and were
referenced to SiMe4. 1H and 13C{ H} NMR signal assignments
1
were confirmed by 1H-COSY and 135-DEPT experiments.
2.2. Ligand synthesis
2.2.1. 2,4,6-Trimethyl-N-(2-thienylmethylene)-aniline (1a)
This ligand has been prepared according to the proce-
dure reported for imine ligands 1b and 1c [8]. A solution of
∗
Corresponding author. Tel.: +43 1 58801 15341; fax: +43 1 58801 15499.
E-mail address: kkirch@mail.zserv.tuwien.ac.at (K. Kirchner).
1381-1169/$ – see front matter © 2006 Elsevier B.V. All rights reserved.
doi:10.1016/j.molcata.2006.04.009

68
J. Wiedermann et al. / Journal of Molecular Catalysis A: Chemical 257 (2006) 67–72
136.3 (thiophene2), 67.0 (N CH2), 22.9 (CH2 CH3), 11.6
(CH3).
2-thiophenecarboxaldehyde (1.25 mL, 13.38 mmol) in 50 mL
of ethanol was treated with 2,4,6-trimethylaniline (1.88 mL,
13.38 mmol). The solution was stirred overnight at room temper-
ature. Upon removal of the solvent a yellow solid was obtained
which was purified by recrystallisation from petroleum ether
and ethyl acetate (1:1). Yield: 2.19 g (71%). Anal. Calcd. for
C14H15NS: C, 73.32; H, 6.59; N, 6.11. Found: C, 73.12; H,
6.69; N, 6.00. 1H NMR (CDCl3): δ 8.32 (s, 1H, N = CH), 7.54 (d,
J = 5.1 Hz, 1H, thiophene), 7.45 (d, J = 3.5 Hz, 1H, thiophene),
7.17 (dd, J = 4.9 Hz, J = 3.8 Hz, 1H, thiophene4), 6.91 (s, 2H,
2.3.4. Dichlorobis-κ-N-[S-(−)-N-(2-thienylmethylene)-1-
phenylethylamine]palladium(II) (3c)
This complex has been prepared analogously to 3a with
1c (0.41 g, 1.90 mmol) and Pd(COD)Cl2 (0.21 g, 0.74 mmol)
as the starting materials. Yield: 0.31 g (85%). Anal. Calcd.
for C26H26Cl2N2PdS2: C, 51.37; H, 4.31; N, 4.61. Found:
C, 51.25; H, 4.21; N, 4.57. 1H NMR (CDCl3): δ 7.80 (d,
J = 4.9 Hz, 1H, thiophene), 7.75 (s, 1H, N = CH), 7.70-7.65 (m,
2H, thiophene and Ph), 7.45–7.31 (m, 4H, Ph-H), 7.15 (dd,
J = 4.9 Hz, J = 3.8 Hz, 1H, thiophene4), 6.22 (q, J = 6.9 Hz, 1H,
N CH CH3), 2.12 (d, J = 7.0 Hz, 1H, N CH CH3). 13C NMR
(CDCl3): δ 162.1 (N C), 139.4 and 136.8 (thiophene2 and Ph1),
138.6, 134.4, and 127.2 (thiophene3,4,5), 128.9, 128.8, and 128.4
(Ph2,3,4,5,6), 69.3 (N CH CH3), 19.9 (N CH CH3).
Ph3,5 H), 2.32 (s, 3H, Ph4 CH3), 2.18 (s, 6H, Ph2,6 CH3). 13
C
NMR (CDCl3): δ 155.6 (N C), 147.9 and 142.6 (thiophene2
and Ph1), 133.0 and 127.3 (Ph2,6 and Ph4), 131.6, 129.9, and
127.6 (thiophene3,4,5), 128.6 (Ph3,5), 20.7 (Ph4 CH3), 18.2
(Ph2,6 CH3).
2.3. Synthesis of palladium complexes
2.3.1. Pd(COD)Cl2
2.3.5. Dichlorobis-κ-N-[N-(2-thienylmethyl)-
aniline]palladium(II) (4)
A suspension of PdCl2 (5.00 g, 28.2 mmol) in methanol
(150 mL) was treated with 1,5-cyclooctadiene (COD) (10.4 mL,
84.6 mmol) and stirred for 48 h at room temperature. During that
time the color of the suspension changed from red to yellow. The
yellow solid was collected on a glass-frit, washed with methanol,
and dried under vacuum. Yield: 7.29 g (91.0%). Spectral data
were identical with those of the authentic sample reported else-
where [10].
This complex has been prepared analogously to 3a with 2
(0.30 g, 1.59 mmol) and Pd(COD)Cl2 (0.09 g, 0.32 mmol) as
the starting materials. Yield: 0.13 g (81%). Anal. Calcd. for
C22H22Cl2N2PdS2: C, 47.53; H, 3.99; N, 5.04. Found: C, 47.77;
H, 4.12; N, 4.89. 1H NMR (CDCl3): δ 7.43–7.25 (m, 5H,
thiophene-H and Ph-H), 7.21–7.15, 7.04–6.99, and 6.88–6.81
(m, 3H, thiophene-H and Ph-H), 5.27 (d, J = 6.3 Hz, 1H, NH),
4.94–4.78 (m, 1H, N CH2), 4.26–4.18 (m, 1H, N CH2). 13C
NMR (CDCl3): δ 143.8 (Ph1), 135.9 (thiophene2), 129.5 (Ph3,5),
129.1, 126.8, 126.7, and 126.6 (thiophene3,4,5and Ph4), 122.0
and 121.9 (Ph2 and Ph6), 51.7 (N CH2).
2.3.2. Dichlorobis-κ-N-[2,4,6-trimethyl-N-(2-
thienylmethylene)-aniline]palladium(II) (3a)
A solution of 1a (0.40 g, 1.74 mmol) in dry toluene was
treated with Pd(COD)Cl2 (0.25 g, 0.87 mmol) and stirred at
70 ◦C for 16 h. The solvent was removed and the crude product
washed three times with diethylether and dried in vacuo. Yield:
0.48 g (87%). Anal. Calcd. for C28H30Cl2N2PdS2: C, 52.88;
2.4. General procedure for the palladium-catalyzed Suzuki
cross-coupling
1
H, 4.75; N, 4.40. Found: C, 53.02; H, 4.65; N, 4.50. H NMR
The substrate (1.00 mmol), phenyl boronic acid (1.5 mmol),
and 2.00 mmol of Cs2CO3 were suspended in 5 mL of dry 1,4-
dioxane, charged with the respective amount of catalyst, and
stirred at 110 ◦C for 18 h. After that, the mixture was cooled
to room temperature and diluted with 10 mL of a 2N aqueous
NaOH solution. The aqueous phase was extracted three times
with dichloromethane, dried over Na2SO4, and evaporated to
dryness. The crude product was purified via column chromatog-
raphy over silica gel (petroleum ether:ethyl acetate (20:1)).
(CDCl3): δ 9.09 (d, J = 1.3 Hz, 1H, N = CH), 7.53 (dd, J = 3.8 Hz,
J = 1.1 Hz, 1H, thiophene), 7.44 (dt, J = 5.1 Hz, J = 1.2 Hz, 1H,
thiophene), 7.00 (dd, J = 5.0 Hz, J = 3.9 Hz, 1H, thiophene4),
6.94 (s, 2H, Ph3,5 H), 2.32 (s, 6H, Ph2,6 CH3), 2.31 (s, 3H
Ph4 CH3). 13C NMR (CDCl3): δ 165.5 (N C), 142.4 and 137.7
(thiophene2 and Ph1), 139.6, 136.4, and 126.8 (thiophene3,4,5),
134.5 (Ph4), 131.3 (Ph2,6), 130.3 (Ph3,5), 21.2 (Ph4 CH3), 19.4
(Ph2,6 CH3).
2.3.3. Dichlorobis-κ-N-[N-(2-thienylmethylene)-1-
propaneamine]palladium(II) (3b)
2.5. X-ray structure determination
This complex has been prepared analogously to 3a with 1b
(0.30 g, 1.96 mmol) and Pd(COD)Cl2 (0.28 g, 0.98 mmol) as
the starting materials. Yield: 0.40 g (85%). Anal. Calcd. for
C16H22Cl2N2PdS2: C, 39.72; H, 4.58; 5.79. Found: C, 39.81;
H, 4.55; 5.58. 1H NMR (CDCl3): δ 8.03 (s, 1H, N = CH),
7.84 (d, J = 5.1 Hz, 1H, thiophene), 7.65 (dd, J = 3.8 Hz,
J = 1.0 Hz, 1H, thiophene), 7.22 (dd, J = 4.9 Hz, J = 3.8 Hz, 1H,
thiophene4), 4.00 (t, J = 7.5 Hz, 2H, N CH2), 2.36–2.21 (m, 2H,
CH2 CH3), 1.06 (t, J = 7.3 Hz, 3H, CH3). 13C NMR (CDCl3)
δ 161.2 (N C), 138.5, 134.2, and 127.3 (thiophene3,4,5),
X-ray data for 3a ClCH2CH2Cl, 3b ClCH2CH2Cl, and
4 were collected on a Bruker Smart CCD area detector
diffractometer using graphi◦te-monochromated Mo K␣ radia-
spheres of the reciprocal space. Corrections for absorption, λ/2
effects, and crystal decay were applied [11]. The structures
were solved by direct methods using the program SHELXS97
[12] structure refinement on F2 was carried out with the pro-
gram SHELXL97 [12]. All non-hydrogen atoms were refined
˚
tion (λ = 0.71073 A) and 0.3 ␻-scan frames covering complete

J. Wiedermann et al. / Journal of Molecular Catalysis A: Chemical 257 (2006) 67–72
69
Table 1
Details for the crystal structure determinations of complexes 3a ClCH2CH2Cl, 3b ClCH2CH2Cl, and 4
3a ClCH2CH2Cl
3b ClCH2CH2Cl
C18 26Cl4N2PdS2
4
Formula
C
30H34Cl4N2PdS2
H
C
22H22Cl2N2PdS2
fw
734.91
582.73
555.84
Crystal size (mm)
Crystal system
Space group
0.63 × 0.38 × 0.17
Monoclinic
C2/c (number 15)
14.0954(6)
10.3528(4)
21.8652(9)
98.874(1)
3152.5(2)
4
1.548
173(2)
1.084
1496
0.29 × 0.24 × 0.197
Monoclinic
P21/c (number 14)
8.8537(3)
13.4687(5)
10.9671(4)
111.226(1)
1219.08(8)
2
1.587
223(2)
1.378
588
0.25 × 0.22 × 0.18
Monoclinic
P21/n (number 14)
6.4398(7)
7.8355(8)
21.922(2)
91.983(2)
1105.5(2)
2
1.670
100(2)
1.282
560
˚
a (A)
˚
b (A)
˚
c (A)
β (◦)
3
˚
V (A )
Z
ρcalc (g cm−3
T (K)
)
µ (mm−1) (Mo K␣)
F(0 0 0)
θmax (◦)
30
30
30
Number of rflns measured
Number of unique rflns
Number of rflns I > 2σ(I)
Number of params
R1 (I > 2σ(I))a
28633
4577
4342
191
13449
3537
3206
122
8641
3192
2994
133
0.0261
0.0225
0.0411
R1 (all data)
0.0276
0.0250
0.0448
wR1 (all data)
Difference of four peaks min/max (eA
0.0683
−0.85/0.67
0.0587
−0.62/0.87
0.0820
−0.59/0.66
−3
˚
)
ꢀ
ꢀ
ꢀ
ꢀ
R1
=
||Fo| − |Fc||/
|Fo|, wR2 = [ (w(Fo2 − Fc2)2)/ (w(Fo2)2)]1/2
.
a
anisotropically. Hydrogen atoms were inserted in idealized posi-
tions and were refined riding with the atoms to which they were
bonded. Salient crystallographic data are given in Table 1. Views
of the Pd complexes, all being centrosymmetric at Pd, are shown
in Figs. 1–3 (primed atoms are inversion related to unprimed
atoms). CCDC 273494, 297222, and 297223 contain the sup-
plementary crystallographic data for this paper. These data can
Fig. 2. Structural view of dichlorobis-␬-N-[N-(2-thienylmethylene)-1-
propaneamine] palladium(II) ClCH2CH2Cl (3b ClCH2CH2Cl) showing
30% thermal ellipsoids (dichloroethane omitted for clarity). Selected bond
◦
Pd Nꢀ 2.018(1); Pd Cl Pd Clꢀ
Pd Nꢀ
˚
lengths (A) and bond angles ( ): Pd
2.3043(4); C(5) 1.276(2);
C(6) 1.473(2); Cl Pd Clꢀ
180.0; Cl Pd Nꢀ 89.51(4).
N
N
N
N
beobtainedfreeofchargefromTheCambridgeCrystallographic
Data Centre via www.ccdc.cam.ac.uk/data request/cif.
Fig. 1. Structural view of dichlorobis-␬-N-[2,4,6-trimethyl-N-(2-thienyl-
methylene)-aniline]palladium(II) ClCH2CH2Cl (3a ClCH2CH2Cl) showing
50% thermal ellipsoids (dichloroethane omitted for clarity). Selected bond
3. Results and discussion
◦
lengths (A) and bond angles ( ): Pd
N
Pd N’ 2.054(2); Pd Cl Pd Clꢀ
˚
2.3010(4); N C(5) 1.289(2); N C(6) 1.442(2); Cl Pd Clꢀ = N Pd Nꢀ 180.0;
Treatment of Pd(COD)Cl2 with ligands 1a–1c and 2 in
toluene for 16 h afforded complexes 3a–3c and 4 cleanly in high
Cl Pd N 89.16(4).

70
J. Wiedermann et al. / Journal of Molecular Catalysis A: Chemical 257 (2006) 67–72
165 ppm. Structural views of 3a, 4b, and 4, as determined by
X-ray crystallography, are depicted in Figs. 1–3. Selected geo-
metric data are reported in the captions. The complexes are in
their trans form and the coordinated imine and amine ligands,
respectively, are coordinated via the nitrogen atoms in mon-
odentate fashion. The molecules display the usual square-planar
coordination around the palladium center. All Pd N and Pd Cl
bond lengths lie within the expected range for trans-N Pd N
and Cl Pd Cl arrangements [13].
Palladiumcomplexescontaining␣-and␤-diimineligandsare
excellent catalysts for the Suzuki coupling [7]. Based on these
findings we were interested in whether palladium complexes
containing monodentate imine as well as amine ligands exhibit
similar reactivities in C C bond coupling reactions. Accord-
ingly, we investigated the activity of 3a–3c and 4 for the coupling
of various aryl bromides with phenyl boronic acid. The results of
this study are summarized in Table 2. In most cases the reactions
were performed with 1 mol% of catalysts in dioxane at 110 ◦C
with 2 equivs of Cs2CO3 acting as base. These conditions have
not been optimized.
The coupling reaction of 4-bromoanisole with phenyl boronic
acid catalyzed by 3a–3c and 4 and a catalyst loading of 1 mol%
afforded 4-methoxybiphenyl in 96, 29, 16, and 35% isolated
yields (entries 1, 4–6). Even with 0.01 mol% of 3a 20% of 4-
methoxybiphenyl are obtained (entry 3). The coupling of the
electronically activated substrate 4-bromoacetophenone with
phenylboronicacidproceedswithallcatalystsresultinginyields
>93% (entries 7–11). Attempts to couple 4-chloroacetophenone
with phenyl boronic acid resulted in almost no conversion (entry
20). While it is difficult to establish a clear trend in the catalytic
activity of complexes 3a–3c and 4 on these preliminary data,
on average, complex 3a shows higher activity than the other
complexes. This is especially apparent in the coupling of the
electronically deactivated and thus more challenging substrate
4-bromoanisole with phenyl boronic acid. This reactivity trend
may suggest that the bulkier mesityl substituent renders the cat-
alyst more active. Finally, the catalytic effect was confirmed
by running the standard reaction on 4-bromoacetophenone and
4-bromoanisole with PdCl2. The reaction proceeds, but led to
much lower yields.
Fig. 3. Structural view of dichlorobis-␬-N-[N-(2-thienylmethyl)-aniline]-
˚
palladium(II) (4) showing 50% thermal ellipsoids. Selected bond lengths (A)
and bond angles (◦): Pd Pd Nꢀ 2.054(2); Pd Cl Pd Clꢀ 2.3090(7);
C(5) 1.455(3); N C(6) 1.499(3); Cl Pd Clꢀ Pd Nꢀ 180.0; Cl Pd
86.38(7).
N
N
N
N
isolated yields (Scheme 1). The synthesis of related dichlorobis-
␬-N-[N-(2-thienylmethylene)-aniline]palladium(II) complexes
has been published recently [13]. It has to be noted that the
synthesis of 3b has been described elsewhere but no spectro-
scopical or X-ray data have been presented [14]. All complexes
are thermally robust yellow solids which are stable to air both
in the solid state and in solution. The identity of the compounds
1
was established by 1H and 13C{ H} NMR spectroscopy, and by
elemental analysis.
From the NMR spectroscopical data it is obvious that the
thienyl moiety is still intact and orthopalladation to form a
chelating ␬2-C,N bound imine ligand, as has been frequently
observed in related systems, did not occur. The NMR spectra
of 3a–3c and 4 bear no unusual features and it is sufficient
to point out that the proton of the imine CH N moiety of the
imineligandsgivesacharacteristicsingletresonanceintherange
1
of 7.75–9.09 ppm. Likewise, in the 13C{ H} NMR spectra the
It has to be noted that recently evidence was presented that
pincer ligands are merely pre-catalysts generating some forms
imine carbon atoms exhibit a singlet resonance between 161 and
Scheme 1.

J. Wiedermann et al. / Journal of Molecular Catalysis A: Chemical 257 (2006) 67–72
71
Table 2
References
Yields of the Suzuki cross-coupling of aryl bromides with phenyl boronic acid
catalyzed by 3a–3c, and 4a
[1] (a) N. Miyaura, A. Suzuki, Chem. Rev. 95 (1995) 2457;
(b) A. Suzuki, in: F. Diederich, P.J. Stang (Eds.), Metal-Catalyzed Cross-
Coupling Reactions, Wiley-VCH, Weinhein, 1998, pp. 49–97, and refer-
ences therein.
[2] (a) H. Weissman, D. Milstein, Chem. Commun. (1999) 1901;
(b) D.A. Alonso, C. Najera, M.C. Pacheco, Org. Lett. 2 (2000)
1823;
(c) J. Dupont, M. Pfeffer, J. Spencer, Eur. J. Inorg. Chem. (2001)
1917;
Entry
Substrate
Catalyst (mol%)
Yield (%)
(d) D.A. Alonso, C. Najera, M.C. Pacheco, J. Org. Chem. 67 (2002)
5588;
(e) L. Botella, C. Najera, Angew. Chem. Int. Ed. 41 (2002) 179;
(f) C. Baleizao, A. Corma, H. Garcıa, A. Leyva, Chem. Commun. (2003)
606;
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
4-Bromoanisole
4-Bromoanisole
4-Bromoanisole
4-Bromoanisole
4-Bromoanisole
4-Bromoanisole
4-Bromoacetophenone
4-Bromoacetophenone
4-Bromoacetophenone
4-Bromoacetophenone
4-Bromoacetophenone
1-Bromo-4-nitrobenzene
1-Bromo-4-nitrobenzene
1-Bromo-4-nitrobenzene
1-Bromo-4-nitrobenzene
2-Bromopyridine
3a (1)
96
68
20
29
16
35
>99
4
>99
93
>99
97
0
95
94
77
61
31b
87
5
3a (0.1)
3a (0.01)
3b (1)
3c (1)
(g) R.B. Bedford, M.E. Blake, C.P. Butts, D. Holder, Chem. Commun.
(2003) 466.
4 (1)
3a (0.01)
3a (0.001)
3b (1)
3c (1)
[3] (a) C. Zhang, J. Huang, M.L. Trudell, S.P. Nolan, J. Org. Chem. 64 (1999)
3804;
(b) C. Zhang, M.L. Trudell, Tetrahedron Lett. 41 (2000) 595;
(c) D.S. McGuinness, K.J. Cavell, Organometallics 19 (2000) 741;
(d) A.M. Magill, D.S. McGuinness, K.J. Cavell, G.J.P. Britovsek, V.C. Gib-
son, A.J.P. White, D.J. Williams, A.H. White, B.W. Skelton, J. Organomet.
Chem. 617 (2001) 546;
(e) A. Fu¨rstner, A. Leitner, Synlett (2001) 290;
(f) W.A. Herrmann, V.P.W. Bo¨hm, C.W.K. Gsto¨ttmayr, J. Organomet.
Chem. 616 (2001) 617;
4 (1)
3a (0.1)
3a (0.01)
3b (1)
3c (1)
3a (1)
3b (1)
3a (1)
2-Bromopyridine
Bromobenzene
Bromobenzene
4-Chloroacetophenone
(g) Y. Zhao, Y. Zhou, D. Ma, J. Liu, L. Li, T.Y. Zhang, H. Zhang, Org.
Biomol. Chem. 1 (2003) 1643;
3a (1)
3a (1)
¨
(h) W.A. Herrmann, K. Ofele, D.V. Preysing, S.K. Scheneider, J.
Organomet. Chem. 687 (2003) 229;
(i) A.-E. Wang, J. Zhong, J.-H. Xie, K. Li, Q.-L. Zhou, Adv. Synth. Catal.
346 (2004) 595;
a
Reaction conditions: 1.0 mmol bromide; 1.5 mmol PhB(OH)2; 2.0 mmol
Cs2CO3; 5 mL dioxane, 110 ◦C; reaction time is 18 h, yields represent isolated
yields (average of at least two experiments) of compounds estimated to be ≥95%
pure as judged by 1H NMR.
(j) I.J.S. Fairlamb, A.R. Kapdi, A.F. Lee, Org. Lett.
4435;
6 (2004)
b
The reaction was stirred at 90 ◦C.
(k) G. Altenhoff, R. Goddard, C.W. Lehmann, F. Glorius, J. Am. Chem.
Soc. 126 (2004) 15195;
(l) N. Hadei, E.A.B. Kantchev, C.J. O’Brien, M.G. Organ, Org. Lett. 7
(2005) 1991;
(m) R. Singh, M.S. Viciu, N. Kramareva, O. Navarro, S.P. Nolan, Org. Lett.
7 (2005) 1829.
of metallic palladium(0) which actually does the catalysis [15].
Pincer ligands possessing only phosphinito donors decomposed
even more easily and lead to more active sources of metallic
palladium. In the present catalytic reactions we cannot exclude
such a possibility since in some cases the formation of palladium
black was observed.
[4] (a) D.A. Albisson, R.B. Bedford, P.N. Scully, S.E. Lawrence, Chem. Com-
mun. (2003) 3002;
(b) J.P. Stambuli, R. Kuwano, J.F. Hartwig, Angew. Chem. (2002)
4746;
(c) J.F. Jensen, M. Johannsen, Org. Lett. 5 (2003) 3025;
(d) C. Baillie, L. Zhang, J. Xiao, J. Org. Chem. 69 (2004) 7779;
(e) F.Y. Kwong, K.S. Chan, C.H. Yeung, A.S.C. Chan, Chem. Commun.
(2004) 2336.
4. Conclusion
We have successfully prepared new palladium(II) com-
plexes containing N-(2-thienylmethylene)-aniline and N-(2-
thienylmethyl)-aniline derived ligands. These complexes were
found to be active as catalysts for Suzuki coupling reactions and
are comparable to related ␣- and ␤-dimine systems, thus repre-
senting an interesting alternative to existing catalytic systems.
Qualitatively, it was found that complexes with imine ligands
featuring sterically demanding substituents such as mesityl are
clearly better catalysts.
[5] (a) A. Zapf, A. Ehrentraut, M. Beller, Angew. Chem. Int. Ed. 39 (2000)
4153;
(b) A. Zapf, R. Jackstell, F. Rataboul, T. Riermeier, Fuhrmann, N. Shaikh,
U. Dingerdissen, M. Beller, Chem. Commun. (2004) 38.
[6] (a) G.Y. Li, Angew. Chem. Int. Ed. 40 (2001) 1513;
(b) R.B. Bedford, Chem. Commun. (2003) 1787;
(c) R.B. Bedford, C.S. Cazin, Chem. Commun. (2001) 987;
(d) R.B. Bedford, C.S. Cazin, S.J. Coles, T. Gelbrich, P.N. Horton, M.B.
Hursthouse, M.E. Light, Organometallics 22 (2003) 2810;
(e) J.-H. Li, W.-J. Liu, Org. Lett. 6 (2004) 2809;
(f) Y. Wang, D.R. Sauer, Org. Lett. 6 (2004) 2793.
[7] (a) G.A. Grasa, A.C. Hillier, S.P. Nolan, Org. Lett. 3 (2001) 1077;
(b) D. Domin, D. Benito-Garagorri, K. Mereiter, J. Fro¨hlich, K. Kirchner,
Organometallics 24 (2005) 3957.
Acknowledgment
[8] B. Ouddaid, M. Ayad, B. Garrigues, Can. J. Chem. 70 (1992)
58.
[9] G. Himbert, K. Diehl, H.-J. Schlindwein, Chem. Ber. 119 (1986)
3227.
¨
Financial support by the “Fonds zur Forderung der wis-
senschaftlichen Forschung” is gratefully acknowledged (Project
No. P16600-N11).

72
J. Wiedermann et al. / Journal of Molecular Catalysis A: Chemical 257 (2006) 67–72
[10] D. Drew, J.R. Doyle, Inorg. Synth. 28 (1990) 346.
[13] W.-S. Hwang, J.-H. Lai, D.-L. Wang, M.Y. Chiang, J. Chin. Chem. Soc. 46
(1999) 529.
[14] R.K.Y. Ho, S.E. Livingstone, Aust. J. Chem. 18 (1965) 659.
[15] (a) W.J. Sommer, K. Yu, J.S. Sears, Y. Ji, X. Zheng, R.J. Davis, C.D. Sherill,
C.W. Jones, M. Weck, Organometallics 24 (2005) 4351;
(b) M.R. Eberhard, Org. Lett. 6 (2004) 2125.
[11] Brukerprograms:SMART, version5.054;SAINT, version6.2.9;SADABS,
version 2.10; XPREP, version 5.1; SHELXTL, version 5.1, Bruker AXS
Inc., Madison, WI, 2001.
[12] G.M. Sheldrick, SHELX97: Program System for Crystal Structure Deter-
mination, University of Go¨ttingen, Go¨ttingen, Germany, 1997.