Pd complexes with trans-chelating ligands composed of two pyridyl groups and rigid π-conjugated backbone

Article abstract of DOI:10.1016/j.poly.2012.04.006

1,2-Bis(2-pyridylethynyl)benzene derivatives, having two pyridyl groups and π-conjugated backbone, were prepared from the 1:2 Sonogashira reaction of 1,2-diiodobenzene with 2-alkynyl pyridines. The obtained ligands react with the palladium(II) complexes such as [PdCl₂(cod)] and [PdCl ₂(MeCN)₂] to form the complexes with the ligands coordinated in a trans-chelating bidentate mode. The ligand obtained from 1,3-diiodobenzene and 2-alkynyl pyridine bridges two Pd(II) centers, yielding a dipalladium complex. A dichloropalladium complex with the trans-chelating ligand, containing two methoxy groups in the central arylene group, promotes coupling of phenyl lithium and of phenyl acetylene to yield the respective homo-coupling products. The ligand displacement reactions of {bis(2-pyridylethynyl)benzene}palladium(II) complex with phosphine and dinitrogen ligands, such as PPh₃, dppe, dppb, en, tmeda, bpy and phen, takes place smoothly to release the trans-chelating ligand.

Full text of DOI:10.1016/j.poly.2012.04.006

Polyhedron 40 (2012) 168–174
Contents lists available at SciVerse ScienceDirect
Polyhedron
journal homepage: www.elsevier.com/locate/poly
Pd complexes with trans-chelating ligands composed of two pyridyl groups
and rigid p-conjugated backbone
⇑
Miso Jung, Yuji Suzaki, Takashi Saito, Kyoichi Shimada, Kohtaro Osakada
Chemical Resources Laboratory, Tokyo Institute of Technology, 4259 R1-3 Nagatsuta, Midori-ku, Yokohama 226-8503, Japan
a r t i c l e i n f o
a b s t r a c t
Article history:
1,2-Bis(2-pyridylethynyl)benzene derivatives, having two pyridyl groups and
p-conjugated backbone,
Received 5 November 2011
Accepted 11 April 2012
Available online 21 April 2012
were prepared from the 1:2 Sonogashira reaction of 1,2-diiodobenzene with 2-alkynyl pyridines. The
obtained ligands react with the palladium(II) complexes such as [PdCl2(cod)] and [PdCl2(MeCN)2] to form
the complexes with the ligands coordinated in a trans-chelating bidentate mode. The ligand obtained
from 1,3-diiodobenzene and 2-alkynyl pyridine bridges two Pd(II) centers, yielding a dipalladium com-
plex. A dichloropalladium complex with the trans-chelating ligand, containing two methoxy groups in
the central arylene group, promotes coupling of phenyl lithium and of phenyl acetylene to yield the
respective homo-coupling products. The ligand displacement reactions of {bis(2-pyridylethynyl)ben-
zene}palladium(II) complex with phosphine and dinitrogen ligands, such as PPh3, dppe, dppb, en, tmeda,
bpy and phen, takes place smoothly to release the trans-chelating ligand.
Keywords:
Bis(2-pyridylethynyl)benzene
Palladium(II) complexes
Trans-chelating ligand
Ó 2012 Published by Elsevier Ltd.
1. Introduction
coordinate with palladium(II) as the trans bidentate ligand [13].
Addition of 1,8-bis(p-(diphenylphosphino)phenyl)anthracene to
Palladium(II) complexes with cis-chelating dinitrogen ligands
such as 2,20-bipyridine (bpy), 1,10-phenanthroline (phen), and N,
N,N0,N0-tetramethyl-1,2-ethylenediamine (tmeda), are commonly
known because of their high stability as well as various chemical
properties [1,2]. The complexes with cis-chelating dinitrogen
ligands catalyze homo-coupling reaction of thiophene [3], cycliz-
ative hydrosilylation of 1,6-dienes [4] and oxidative cyclocarbony-
lation of b-aminoalcohols [5] as well as the cyclization and
polymerization of dienes [6,7]. The dinitrogen ligands are em-
ployed for the Pd-catalyzed copolymerization of olefin and CO to
yield the polyketone [8]. Brookhart et al. discussed detailed mech-
anism of the [PdCl2(bpy)]-catalyzed co-polymerization, which in-
cludes alternating insertion of the two different monomers [9].
Organopalladium(II) complexes having the ligand with extended
the palladium-catalyzed Mizoroki–Heck reaction of cyclohexene
and aryl bromides results in high regioselectivity of the product.
1,2-Bis(2-pyridylethynyl)benzene is a dinitrogen ligand first em-
ployed by Bosch et al. [14], and is used as the ligand for mononu-
clear and oligonuclear complexes of Ag [14], Cu [15], Co [16], Zn
[16], Rh [17] and Pd [14,18]. Recently we reported the dipalladium
complexes with a [3]rotaxane structure, composed of the crown
ethers bearing palladium(II)(dichloro){1,2-bis(2-pyridylethynyl)
benzene} unit and its catalytic properties for the cyclizative Mizor-
oki–Heck reactions of difunctionalized substrates [19]. Here we
report the synthesis of the substituted 1,2-bis(2-pyridylethy-
nyl)benzene derivatives and their palladium(II) complexes as well
as their reactivity. Formation of a dinuclear Pd(II) complex of 1,3-
bis(2-pyridylethynyl)benzene is also mentioned.
p-conjugated system were reported to show fluorescence in solu-
tion as well as in the solid state [10]. Recent interest in the oligo-
pyridine ligand for Pd(II) complex is in its use as the building
blocks of the supramolecules [11]. The amphiphilic (1,2-ethylene-
diamine)palladium(II) bearing N-alkylbipyridinium ligands were
2. Results and discussion
2.1. Preparation of bis(2-pyridylethynyl)benzene ligands and their
Pd(II) complexes
reported to form micelle and [5]rotaxanes with
a-cyclodextrins
in water [12]. The Pd complexes with trans-chelating dinitrogen li-
gands are much less common than that of the cis-chelating ligands.
Gelman et al. reported that 1,8-bis(diisopropylphosphino)tripty-
Chart 1 lists the palladium(II) complexes, 1a–1h, 3, and their li-
gands 2a, 2d, 2f–2h, 4.
Ligands, 2d and 2f–2h, have the substituents on the pyridyl or
phenylene group.
cene
and
1,8-bis(p-(diphenylphosphino)phenyl)anthracenes
Table 1 summarizes the synthesis of o-{bis(2-pyridylethy-
nyl)arene}, 2a and 2d, by Sonogashira coupling reaction. Reaction
of 1,2-diiodobenzene (5a) and 2-ethynylpyridine in 0.5 M
⇑
Corresponding author.
E-mail address: kosakada@res.titech.ac.jp (K. Osakada).
0277-5387/$ - see front matter Ó 2012 Published by Elsevier Ltd.
http://dx.doi.org/10.1016/j.poly.2012.04.006

M. Jung et al. / Polyhedron 40 (2012) 168–174
169
R1
R1
R2
diiodo-4,5-dimethoxybenzene (5b) yields 2d in 92% yield (run 3).
1,2-Dibromobenzene (5c) showed much lower reactivity than 5a
and its reaction with 2-ethynylpyridine yielded 2a in low yields
(0–16%, run 4–6). The Pd/tBu-X-Phos (X-Phos = 2-di-tert-butyl-
phosphino-20,40,60-triisopropylbiphenyl) catalyst (run 6) led to bet-
ter yield than the reaction using triarylphosphines.
Eq. (1) shows synthesis of 1,2-{bis(2-pyridylethynyl)benzene}
derivatives, 2f–2h, having substituents on the pyridyl groups from
Sonogashira reaction of 1,2-dialkynylbenzene with 2-bromopyri-
dines, 6f–6h.
N
R2
X
N
R3
R3
R3
R3
X
Pd
N
R2
N
2a, 2d, 2f, 2g, 2h
N
R2
R1
R1
1a-1h
N
N
Pd
Cl
Cl
Cl
N
Cl
N
Pd
N
3
4
compund R1
R2
R3
X
1a, 2a
1b
1c
1d, 2d
1e
1f, 2f
1g, 2g
1h, 2h
H
H
H
H
H
H
H
Br
H
H
H
H
H
H
H
OMe
OMe
H
Cl
Br
OAc
Cl
OAc
Cl
ð1Þ
H
Me
CH2OPh
H
H
H
Cl
Cl
Chart 1. Pd(II) complexes 1a–1h and 3 and their ligands 2a, 2d, 2f–2h and 4.
1,3-{Bis(2-pyridylethynyl)benzene}, 4, is synthesized from 1,3-
diiodobenzene and 2-ethynylpyridine by a similar procedure to
that of 2a (Eq. (2)).
Table 1
Synthesis of 1,2-bis(2-pyridylethynyl)benzene 2a, 2b.a
N
PdCl2(PPh3)2
CuI, NH3(aq)
I
I
N
+ 2
ð2Þ
THF, r.t.
N
4 (42%)
Table 2 summarizes synthesis of palladium(II) complexes 1a–
1h. [PdCl2(MeCN)2], [PdCl2(cod)], [PdBr2(cod)], and Pd(OAc)2 were
employed as the starting complexes. Reaction of 2a and
[PdCl2(MeCN)2] in CH2Cl2/MeCN yields 1a in 60%, while using
[PdCl2(cod)] results in quantitative formation of the product
(99%). 1,2-Bis(2-pyridylethynyl)benzene palladium(II) complex,
bearing bromo and acetoxy ligands, 1b and 1c, were similarly syn-
thesized from the reaction of 2a with [PdBr2(cod)], and with
Pd(OAc)2, respectively. Fig. 1 depicts molecular structures of 2a,
1f, and 1g determined by X-ray crystallography. 1,2-{Bis(2-pyri-
dylethynyl)benzene} (2a) adopts a distorted planar conformation
with torsion angle C7–C8–C13–C14 of 2.9° (Fig. 1A). Complex 1f
was determined as a square planar four-coordinated complex bear-
ing trans-chelating-1,2-{bis(2-pyridylethynyl)benzene}. Palla-
dium, carbon, and nitrogen atoms of 1f are included in a plane
with C8–C9–C14–C15 torsion angle of 0.2°. Complex 1g contains
a crystallographic 2-fold axis in the molecule and its dinitrogen li-
gand has conformation of the backbone to the ligand of 1f.
Run
5a-5c
Base/solvent
Temp./time
Yield
1
2
3
5a
5a
5b
5c
5c
5c
0.5 M NH3(aq)/THF
Ethanolamine/THF
0.5 M NH3(aq)/THF
Ethanolamine/THF
Et3N/DMF
r.t./94 h
50 °C/14 h
r.t./24 h
r.t./24 h
100 °C/46 h
100 °C/18 h
2a, >99%
2a, 83%
2d, 92%
2a, 0%
2a, 5%
2a, 16%
4b
5c
6d
Et3N/DMF
a
b
c
[PdCl2(PPh3)2], 2 mol%; CuI, 4 mol%.
[PdCl2(PPh3)2], 3 mol%; CuI, 2 mol%.
[PdCl2(MeCN)2], 5 mol%; CuI, 10 mol%; P(C6H4-2-Me)3, 15 mol%.
d
[PdCl2(MeCN)2], 5 mol%; CuI, 10 mol%; P-tBu2(C6H4-2-C6H4-2,4,6-iPr) (tBu-X-
phos) 15 mol%.
Fig. 2A and B compares 1H NMR spectra of 2f and 1f. The pyridyl
(d 7.57, 7.74, 7.95) and phenylene (d 7.69, 7.90) hydrogen peaks of
NH3(aq)/THF [20] at room temperature or in ethanolamine/THF at
50 °C gave 2a in good yields (run 1, 2). A similar reaction using 1,2-

170
M. Jung et al. / Polyhedron 40 (2012) 168–174
Table 2
Synthesis of {1,2-bis(2-pyridylethynyl)benzene}palladium(II) complexes.
Run
Ligand, 2a, 2d, 2f–2h
PdX2L2
Solvent
Temp./time
Yield
R1
R2
R3
1
2
3
4
5
6
7
8
9
10
2a
2a
2a
2a
2d
2d
2d
2f
H
H
H
H
H
H
H
H
H
Br
H
H
H
H
H
H
H
Me
H
H
H
H
OMe
OMe
OMe
H
H
H
[PdCl2(MeCN)2]
[PdCl2(cod)]
[PdBr2(cod)]
Pd(OAc)2
[PdCl2(MeCN)2]
[PdCl2(cod)]
Pd(OAc)2
[PdCl2(MeCN)2]
[PdCl2(MeCN)2]
[PdCl2(MeCN)2]
CH2Cl2/MeCN
CHCl3
dmso
Toluene
CH2Cl2/MeCN
CHCl3
r.t./24 h
1a, 60%
1a, 99%
1b, 80%
1c, 77%
1d, 60%
1d, 99%
1e, 75%
1f, 93%
1g, 96%
1h, 90%
50 °C/42 h
50 °C/2 h
r.t./15 min
r.t./72 h
50 °C/98 h
r.t./10 min
r.t./48 h
Toluene
CH2Cl2/MeCN
CH2Cl2/MeCN
CH2Cl2/MeCN
2g
2h
CH2OPh
H
r.t./13 h
r.t./3 h
Fig. 2. 1H NMR spectra of (A) 2f, (B) 1f and (C) 3 (300 MHz, r.t., dmso-d6). The
labeling assigned to the hydrogens of compound 3 is given in the Eq. (3).
Fig. 1. Molecular structures of (A) 2a, (B) 1f and (C) 1g with 50% of probability. The
hydrogen atoms and incorporated solvent molecule of 1f are omitted.
Reaction of 4 with [PdCl2(cod)] in CHCl3 yields dinuclear com-
plex 3 in 55% yield (Eq. (3)). The structure of 3 was determined
by NMR and mass spectroscopy as well as elemental analysis.
FAB mass spectrum of 3 contains peaks at m/zꢀ87+8 and 703, as-
signed to [3-Clꢀ]+ (Calc. 876.9) and [3-PdCl3
]
(Calc. 702.5),
1f are observed at lower magnetic field position than those of 2f (d
respectively.
7.11, 7.33, 7.55, 7.64).

M. Jung et al. / Polyhedron 40 (2012) 168–174
171
2.2. Reactions of phenyllithium and phenylacetylene with bis(2-
pyridylethynyl)benzene palladium(II) complex
The homo-coupling reaction of aryl-metal reagents and of ter-
minal alkynes were studied by using various transition metal catal-
ysis [21,22]. Previously, we reported the quantitative formation of
biaryls from the intermolecular reaction of the cationic arylpalladi-
um and arylnickel complexes with 2,20-bipyridine ligand [23,24].
The reaction of PhLi with 1d also takes place to produce biphenyl
as shown in Scheme 1. The reaction of phenylacetylene with 1d un-
der basic conditions yields the corresponding diyne in 10%.
Although the trans-chelating ligand of 1d may prevent smooth
reductive elimination of the homocoupling product from a dior-
ganopalladium(II) intermediate generated from the reaction of 1d
with the organometallic reagent, the products are obtained in con-
siderable yields.
ð3Þ
2.3. Reactions of auxiliary cis-coordinating ligands with 1,2-bis(2-
pyridylethynyl)benzene palladium(II) complexes
Ligand displacement reactions starting from the Pd(II) com-
plexes such as [PdCl2(cod)] and [PdCl2(MeCN)2] bearing relatively
labile ligands were widely employed as the synthesis of the corre-
sponding dichloropalladium complexes with other auxiliary li-
gands. The ligand displacement reaction provides information on
the stability of the coordination bonds of these ligands.
1H NMR spectrum of 3 (Fig. 2C) shows seven signals each of
which is assigned to the hydrogen of two equivalent 1,3-{bis(2-
pyridylethynyl)benzene} ligands. Peak due to the hydrogen at 6-
position of the pyridyl group of 3 (d 9.06) is observed at lower mag-
netic field position than that of 4 (d 8.59).
The reaction of PPh3 with 1d yields a mixture of 2d (74%)
and [PdCl2(PPh3)2] (Table 3, run 1). Similar reactions using
Ph2P(CH2)2PPh2 (dppe) and Ph2P(CH2)4PPh2 (dppb) form
[PdCl2(dppe)] and [PdCl2(dppb)], respectively (run 2, 3). The reac-
tions of dinitrogen ligands, such as tmeda (N,N,N0,N0-tetramethyl-
ethylenediamine), en (ethylenediamine), 2,20-bpy and phen with
1d at 100 °C yield the corresponding Pd(II) complexes with the
cis-chelating ligand in high yield (95–97%). The reaction of 1d with
2a at 100 °C gave a mixture of 1a, 1d, 2a and 2d after 65 h (run 8).
No replacement was observed in the reaction of py, cod and dmso
with 2d. These results indicate that 1,2-bis(2-pyridylethynyl)ben-
zene coordinates to Pd(II) more strongly than with py, cod and
dmso and less strongly than with phosphine and dinitrogen ligands,
as shown in Table 3.
N
Cl Pd Cl
N
PhLi
MeO
MeO
CHCl3
50 oC, 24 h
44%
10%
1d
Ph
CuI, Et3N
Ph
Ph
THF
r.t., 24 h
Scheme 1. Reactions of 1d with phenyllithium and with phenylacetylene.
3. Conclusion
Palladium(II) complexes bearing 1,2- and 1,3-bis(2-pyridylethy-
nyl)benzene ligands were obtained and their structure and reactiv-
ity have been studied. The ligand exchange reaction starting from
[PdCl2(cod)] and 1,2-bis(2-pyridylethynyl)benzenes yields corre-
sponding dichloropalladium (II) complex in high yield. The reac-
tion of [PdCl2(MeCN)2] and 1,3-bis(2-pyridylethynyl)benzenes
causes 2:2 complexation to generate the dinuclear Pd(II) complex.
{1,2-Bis(2-pyridylethynyl)benzene}palladium complex reacts with
PhLi and with phenylacetylene to give biphenyl and diyne, respec-
tively. The ligand displacement reactions revealed that the 1,2-
bis(2-pyridylethynyl)benzene is a weaker ligand than the phos-
phine and the cis-chelating dinitrogen ligands, such as PPh3, dppe,
dppb, en, tmeda, bpy and phen.
Table 3
Ligand exchange of 1d.
Run
L2
Temp./time
Yield of PdCl2L2
1
2PPh3
r.t./22 h
r.t./30 min
r.t./30 min
100 °C/30 min
100 °C/10 min
100 °C/50 min
100 °C/10 min
100 °C/65 h
100 °C/6 days
50 °C/30 h
74%a
>99%
75%
95%
97%
64%
87%
57%
2
3
4
5
Ph2P(CH2)2PPh2 (dppe)
Ph2P(CH2)4PPh2 (dppb)
Me2N(CH2)2NMe2 (tmeda)
H2N(CH2)2NH2 (en)
2,20-bpy
6
4. Materials and methods
7
1,10-phen
8
1a
4.1. General
9
10
11
Pyridine (py)
cod
dmso-d6
No reaction
No reactionb
No reactionc
100 °C/47 h
[PdX2(cod)] (X = Cl, Br) [25] and 1,2-diethynylbenzene [26]
were prepared according to the literature method. The other chem-
icals were commercially available and used without further purifi-
cation. 1H and 13C{1H} NMR spectra were recorded on Varian
a
b
c
Reaction in CH2Cl2.
Reaction in CDCl3.
Reaction in dmso-d6.

172
M. Jung et al. / Polyhedron 40 (2012) 168–174
MERCURY300 and JEOL EX-400 spectrometers. IR absorption spec-
tra were recorded on Shimadzu FT/IR-8100 spectrometers. Fast
atom bombardment mass spectrum (FABMS) was obtained from
JEOL JMS-700 (matrix, glycerol or m-nitrobenzyl alcohol). Elemen-
tal analysis was carried out with a LECO CHNS-932 CHNS or Yanaco
MT-5 CHN autorecorder at the Center for Advanced Materials Anal-
ysis, Technical Department, Tokyo Institute of Technology.
H), 7.22 (s, 2 H, C6H2), 7.28 (dd, C5H4N, 2 H, J = 8.1, 7.4 Hz), 7.59
(d, C5H4N, 2 H, J = 7.4 Hz), 7.74 (dd, C5H4N, 2 H, J = 8.1, 7.7 Hz),
9.50 (m, 2 H, C5H4N). Anal. Calc. for C26H22N2O6Pdꢁ(H2O)0.5: C,
54.41; H, 4.04; N, 4.88. Found: C, 54.45; H, 4.03; N, 4.73%.
4.1.6. Dichloro-{1,2-bis[(6-methyl-2-
pyridyl)ethynyl]benzene}palladium (1f)
The ligand 2f (30.8 mg, 0.10 mmol) was dissolved in CH2Cl2
(1.0 mL). A solution of [PdCl2(MeCN)2] (39 mg, 0.15 mmol) in
MeCN-CH2Cl2 (1:1) (4.0 mL) was prepared separately. The MeCN–
CH2Cl2 (1:1) solution was carefully layered over the CH2Cl2 solu-
tion, and the reaction mixture was placed in the dark. After 2 days
yellow crystals of 1f were formed which were collected by filtra-
tion, washed with CHCl3 and dried in the atmosphere. Yield:
46 mg (93%). 1H NMR (300 MHz, dmso-d6, r.t.) d = 3.51 (s, 6 H),
7.57 (d, 2 H, J = 6.6 Hz), 7.69 (dd, 2 H, J = 5.8, 3.6 Hz), 7.74 (d, 2 H,
J = 6.6 Hz), 7.90 (dd, 2 H, J = 5.8, 3.6 Hz), 7.95 (t, 2 H, J = 7.7 Hz).
4.1.1. Dichloro-(1,2-bis(20-pyridylethylnyl)benzene)palladium (1a)
[14]
A solution of [trans-PdCl2(MeCN)2] (87.9 mg, 0.34 mmol) in
MeCN (10 mL) was carefully layered over
a solution of 2f
(76.8 mg, 0.27 mmol) in CH2Cl2 (3 mL). The mixture was sealed
and allowed to stand in the dark. Clear yellow precipitate was
formed after 24 h. The resulting solid was collected by filtration,
washed with MeCN and dried in vacuo to form 1a as yellow solid.
Yield: 75 mg (60%). IR (KBr disk, r.t.)
m 3060, 3023, 2221 (C„C),
1596, 1495 cmꢀ1
.
MS (FAB pos): m/z = 452 ([MꢀClꢀ]+). IR (KBr disk, r.t.)
m 3066,
2211 (C„C), 1566, 1467, 1238 cmꢀ1
.
4.1.2. Dibromo-{1,2-bis[(2-pyridyl)ethynyl]benzene}palladium (1b)
A mixture of 1a (280 mg, 1.0 mmol) and [PdBr2(cod)] (187 mg,
0.50 mmol) in dmso (4.0 mL) was stirred for 2 h at 50 °C. A yellow
solid, separated from the solution, was collected by filtration. The
product was washed with toluene and hexane and then dried un-
der reduced pressure to give 1b. Yield: 218 mg (80%). 1H NMR
(300 MHz, CDCl3, r.t.) d = 7.36 (ddd, C5H4N, 2 H, J = 7.4, 5.8,
1.7 Hz), 7.51 (dd, C6H4, 2 H, J = 5.8, 3.3 Hz), 7.66 (d, C5H4N, 2 H,
J = 7.7 Hz), 7.75-7.81 (m, 4 H, C5H4N, C6H4), 8.89 (d, 2 H, C5H4N,
4.1.7. Dichloro-{1,2-bis[(6-phenoxymethyl-2-
pyridyl)ethynyl]benzene}palladium (1g)
Ligand 2g (19 mg, 0.04 mmol) was dissolved in CH2Cl2 (1.0 mL),
and a solution of [PdCl2(MeCN)2] (16 mg, 0.059 mmol) in 2.0 mL of
MeCN–CH2Cl2 (1:1) was prepared, separately. The MeCN–CH2Cl2
(1:1) solution was carefully layered over the CH2Cl2 solution and
the vial capped and placed in the dark. After 13 h, the yellow crys-
tals of 1g, formed were collected by filtration, washed with CH2Cl2
and dried in the atmosphere. Yield: 26 mg (96%). MS (FAB pos) m/
z = 635 ([MꢀClꢀ]+). Anal. Calc. for C34H26Cl2N2PdꢁH2O: C, 59.36; H,
3.81; N, 4.07. Found: C, 60.12; H, 4.06; N, 4.21%.
J = 5.8 Hz). MS (ESI pos): m/z = 466.9 ([M-Br]+). IR (KBr disk, r.t.)
3058, 3021, 2220 (C„C), 1596, 1494, 759 cmꢀ1
m
.
4.1.3. Diacetoxy-{1,2-bis[(2-pyridyl)ethynyl]benzene}palladium (1c)
A toluene (13 mL) solution of Pd(OAc)2 (140 mg, 0.62 mmol)
was added to toluene (8.0 mL) solution of 1a (179 mg,
4.1.8. Dichloro-{1,2-bis[(5-bromo-2-
pyridyl)ethynyl]benzene}palladium (1h)
a
0.64 mmol), and the mixture was stirred for 1 h at room tempera-
ture. The brown solid, separate from the solution, was collected by
filtration, washed with toluene and hexane, and then dried under
reduced pressure to give 1c. Yield: 241 mg (77%). 1H NMR
(300 MHz, CDCl3, r.t.) d = 1.67 (s, Me, 6 H), 7.34 (ddd, C5H4N, 2 H,
J = 7.4, 5.5, 1.6 Hz), 7.53 (dd, C6H4, 2 H, J = 5.8, 3.3 Hz), 7.63 (d,
C5H4N, 2 H, J = 7.1 Hz), 7.76 (ddd, C5H4N, 2 H, J = 7.7, 7.7, 1.7 Hz),
The ligand 2h (131 mg, 0.29 mmol) was dissolved in CH2Cl2
(3.0 mL) and a separate solution of [PdCl2(MeCN)2] (104 mg,
0.39 mmol) in MeCN (13 mL) was prepared. The MeCN solution
was carefully layered over the CH2Cl2 solution and the vial capped
and placed in the dark. Clear yellow precipitate was formed after
3 h. The resulting solid was collected by filtration, washed with
CHCl3 and dried in vacuo to form 1h as brown solid. Yield:
170 mg (90%). MS (FAB pos) m/z = 581 ([MꢀClꢀ]+). 1H NMR
(400 MHz, CD2Cl2, r.t.) d = 6.96 (t, 2 H, J = 7.2 Hz), 7.12 (dd, 2 H,
J = 8.0, 2.4 Hz), 7.23 (t, 4 H, J = 7.6 Hz), 7.64-7.60 (m, 6 H), 7.65
(d, 2 H, J = 6.8 Hz), 7.59 (dd, 2 H, J = 3.2, 6.0 Hz), 7.83 (t, 2 H,
J = 4.8 Hz), 7.86 (dd, 2 H, J = 3.2, 5.6 Hz). MS (FAB pos): m/z = 461
7.80 (dd,
2 H, C6H4, J = 5.8, 3.3 Hz), 9.51 (d, 2 H, C5H4N,
J = 5.8 Hz). MS (FAB pos): m/z = 446 ([MꢀClꢀ]+). IR (KBr disk, r.t.)
m
3105, 3070, 2222 (C„C), 1628, 1327 cmꢀ1. Anal. Calc. for
24H18N2O4PdꢁH2O: C, 55.13; H, 3.86; N, 5.36. Found: C, 55.01; H,
C
3.81; N, 5.01%.
([Mꢀ2(Cl)]+). IR (KBr disk, r.t.)
m 3055, 2223 (C„C), 1494, 1230,
4.1.4. Dichloro-{1,2-dimethoxy-4,5-bis(20-
759 cmꢀ1
.
pyridylethynyl)benzene}palladium (1d) [18c]
Ligand 2d (510 mg, 1.5 mmol) was dissolved in 21 mL of CH2Cl2.
A solution of [PdCl2(MeCN)2] (580 mg, 2.2 mmol) in MeCN (68 mL)
was prepared separately, and was carefully layered over the CH2Cl2
solution of 2d. The reaction mixture was placed in the dark. Clear
yellow precipitate was formed after 72 h. The resulting solid was
collected by filtration, washed with MeCN and dried in vacuo to
form 1d as yellow solid. Yield: 500 mg (60%).
4.1.9. 1,2-Bis(20-pyridylethynyl)benzene (2a) [14]
A mixture of 1,2-diiodobenzene (3.3 g, 10 mmol), 2-ethynylpyr-
idine (2.3 g, 22 mmol), [PdCl2(PPh3)2] (140 mg, 0.20 mmol) and CuI
(76 mg, 0.40 mmol) in THF (120 mL) and 0.5 M aqueous ammonia
(80 mL) was stirred under argon at room temperature for 94 h.
After evaporation of the solvent, the obtained oily residue was dis-
solved in CH2Cl2, The solution was washed with water, and was
dried over MgSO4. After removing MgSO4 and subsequent evapora-
tion of the solvent, the obtained residue was purified by chroma-
tography on silica gel eluting with CH2Cl2. Yield: 3.6 g (>99%). IR
4.1.5. Diacetoxy-{1,2-dimethoxy-4,5-bis(20-
pyridylethynyl)benzene}palladium (1e)
A toluene (15 mL) solution of Pd(OAc)2 (140 mg, 0.62 mmol)
(KBr disk, r.t.)
4.2. 1,2-Dimethoxy-4,5-bis(20-pyridylethynyl)benzene (2d) [18c]
mixture of 1,2-diiodo-4,5-dimethoxybenzene (1.2 g,
m .
3057, 2220 (C„C), 1579, 1460, 773 cmꢀ1
was added to
a toluene (10 mL) solution of 1b (218 mg,
0.64 mmol), and the mixture was stirred for 10 min at room tem-
perature. The brown solid, separated from the solution, was col-
lected by filtration, washed with acetone and Et2O, and then
dried under reduced pressure to give 1e. Yield: 272 mg (75%). 1H
NMR (300 MHz, CDCl3, r.t.) d = 1.67 (s, OAc, 6 H), 4.02 (s, OMe, 6
A
3.0 mmol), 2-ethynylpyridine (680 mg, 12 mmol), [PdCl2(PPh3)2]
(42.0 mg, 0.059 mmol) and CuI (23.0 mg, 0.12 mmol) in THF

M. Jung et al. / Polyhedron 40 (2012) 168–174
173
(36 mL) and 0.5 M aqueous ammonia (24 mL) was stirred at room
4.6. Complex 3 [27]
CHCl3 solution (30 mL) of
temperature for 24 h. After evaporation of the solvent, the oily res-
idue was dissolved in CH2Cl2. The organic layer was washed with
water, dried over MgSO4 and filtered, and the solvent was evapo-
rated. The residue was purified by chromatography on silica gel
eluting with CH2Cl2. Yield: 940 mg (92%).
A
4
(168 mg, 0.60 mmol) and
[PdCl2(cod)] (155 mg, 0.60 mmol), was stirred at 50 °C for 24 h.
The resulting solid was collected by filtration, washed with CHCl3
and dried in vacuo to form 3 as yellow solid. Yield: 298 mg
(55%). 1H NMR (300 MHz, dmso-d6, r.t.) d = 7.44 (t,
2 H,
J = 8.3 Hz), 7.62 (t, 4 H, J = 7.4 Hz), 7.72 (d, 4 H, J = 7.7 Hz), 7.87
(d, 4 H, J = 7.7 Hz), 8.04 (t, 4 H, J = 7.7 Hz), 8.30 (s, 2 H), 9.06 (d, 4
H, J = 5.2 Hz). MS (FAB pos): m/z = 878 ([MꢀClꢀ]+). IR (KBr disk,
4.3. 1,2-Bis[(6-methyl-2-pyridyl)ethynyl]benzene (2f)
r.t.)
m . Anal. Calc. for
3063, 2219 (C„C), 1487, 1362 cmꢀ1
A Et3N solution (15 mL) of 6-bromo-2-picoline (6f) (69 mg,
4.0 mmol), CuI (13 mg, 0.068 mmol), [PdCl2(PPh3)2] (48 mg,
0.068 mmol), 1,2-diethynylbenzene (200 mg, 1.7 mmol) was
stirred for 12 h at 80 °C. The resulting solid was removed by filtra-
tion, which was followed by evaporation of the filtrate. The ob-
tained solid was washed with hexane to give 2f as white solid.
Yield: 267 mg (52%). 1H NMR (400 MHz, CDCl3, r.t.) d = 2.59 (s, 6
H), 7.11 (dd, 2 H, J = 5.6, 3.2 Hz), 7.33 (dd, 2 H, J = 5.6, 3.2 Hz),
7.55 (m, 4 H), 7.64 (dd, 2 H, J = 5.6, 3.2 Hz). 13C NMR (75.5 MHz,
CDCl3, r.t.): d 24.5, 87.4, 93.1, 122.6, 124.8, 125.5, 128.5, 132.0,
136.2, 142.6, 158.8. Anal. Calc. for C22H16N2: C, 85.69; H, 5.23; N,
9.08. Found: C, 85.81; H, 5.04; N, 9.06%. MS (ESI pos): m/
C40H24Cl4N4Pd2: C, 52.49; H, 2.64; N, 6.12; Cl, 15.49. Found: C,
52.71; H, 2.87; N, 6.10; Cl, 15.51%.
4.7. 1,3-Bis(30-pyridylethynyl)benzene (4)
A mixture of 1,3-diiodobenzene (3.30 g, 10 mmol), 2-ethynyl-
pyridine (113 mg, 22 mmol), [PdCl2(PPh3)2] (140 mg, 0.10 mmol)
and CuI (76.0 mg, 0.39 mmol) in THF (120 mL) and 0.5 M aqueous
ammonia (80 mL) was stirred under argon at room temperature for
30 h. After evaporation of the solvent, the oily residue was dis-
solved in AcOEt and washed with saturated aqueous NH4Cl and
brine. The organic layer was dried over MgSO4 and filtered, and
the solvent was evaporated. The residue was purified by chroma-
tography on silica gel eluting with CH2Cl2–AcOEt to give 4 as
brown solid. Yield: 2.67 g (96%). 1H NMR (300 MHz, CDCl3, r.t.)
d = 7.22 (dd, 2 H, J = 7.4, 4.9 Hz), 7.33 (t, 1 H, J = 7.7 Hz), 7.50 (d, 2
H, J = 7.7 Hz), 7.57 (d, 2 H, J = 7.7 Hz), 7.66 (dt, 2 H, J = 7.7,
z = 331.1 ([M+Na]+). IR (KBr disk, r.t.)
m 3046, 2210 (C„C), 1580,
1449, 788 cmꢀ1. Anal. Calc. for C22H16N2: C, 85.69; H, 5.23; N,
9.08. Found: C, 85.81; H, 5.04; N, 9.06%.
4.4. 1,2-Bis[(6-phenoxymethyl-2-pyridyl)ethynyl]benzene (2g)
1.4 Hz), 7.79 (s, 1 H), 8.59 (d, 2 H, J = 4.9 Hz). IR (KBr disk, r.t.)
m
3049, 2214 (C„C), 1579, 1458, 781 cmꢀ1
.
A Et3N solution (11 mL) of 2-bromo-6-(phenoxymethyl)pyri-
dine (6g) (528 mg, 2.0 mmol), CuI (7.0 mg, 0.037 mmol),
[PdCl2(PPh3)2] (24.0 mg, 0.034 mmol), 1,2-diethynylbenzene
(100 mg, 0.78 mmol) was stirred at 50 °C for 24 h, the reaction
mixture was cooled to room temperature. The resulted solid was
removed by filtration. The filtrate was evaporated to dryness under
reduced pressure to give crude product. The oily residue was dis-
solved in AcOEt, and the resulting solution was washed with satu-
rated aqueous NH4Cl, H2O and brine. The organic layer was dried
over MgSO4 and filtered, and the solvent was evaporated. The oily
residue was purified by chromatography on silica gel eluting with
AcOEt–hexane to give 2g. Yield: 336 mg (88%). 1H NMR (300 MHz,
CDCl3, r.t.) d = 5.24 (s, 4 H), 6.96-6.99 (m, 6 H), 7.30 (t, 4 H,
J = 8.0 Hz), 7.39 (dd, 2 H, J = 5.8, 3.3 Hz), 7.50 (dd, 2 H, J = 6.3,
2.2 Hz), 7.63–7.70 (m, 6 H).
4.8. Reaction of phenyllithium with 1d
A cyclohexane–diethylether solution of PhLi (1.09 M, 0.42 mL)
was added to the CHCl3 (20 mL) solution of 1d (26 mg, 0.05 mmol).
The mixture was stirred for 24 h at 50 °C then cooled to room tem-
perature. The reaction was stopped by addition of water and CHCl3
to the mixture. Separated organic phase was washed with water,
dried over MgSO4, and dried under reduced pressure to form
biphenyl (35 mg, 0.022 mmol, 44%). The product was determined
by 1H NMR spectroscopy.
4.9. Reaction of ethynylbenzene with 1d
Et3N (2.0 mL, 0.014 mmol), CuI (2.0 mg, 1.0 ꢂ 10ꢀ3 mmol) and
ethynylbenzene (0.022 mL, 0.20 mmol) was added to the THF
(2.0 mL) solution of 1d (52 mg, 0.10 mmol). The mixture was stir-
red for 20 h at room temperature. The solid separated from the
solution was removed by filtration. The solvent was evaporated
to from the crude product which is dissolved in Et2O then washed
with water. The separated organic phase was dried over MgSO4
then evaporated to form the product which is analyzed by 1H
NMR spectroscopy. The product contains 1,4-diphenylbutadiene
(10%) and 2d (30%).
4.5. 1,2-Bis[(5-bromo-2-pyridyl)ethynyl]benzene (2h)
A Et3N solution (15 mL) of 2,5-dibromopyridine (6h) (948 mg,
4.0 mmol), CuI (13.0 mg, 0.068 mmol), [PdCl2(PPh3)2] (48.0 mg,
0.068 mmol), 1,2-diethynylbenzene (200 mg, 1.7 mmol) was stir-
red at 80 °C for 24 h, the reaction mixture was cooled to room tem-
perature, and then filtration was applied. The filtrate was
evaporated to dryness under reduced pressure to give an oily res-
idue. The oily residue was dissolved in AcOEt, and the resulting
solution was washed with saturated aqueous NH4Cl and brine.
The organic layer was dried over MgSO4 and filtered, and the sol-
vent was evaporated. The oily residue was purified by chromatog-
raphy on silica gel eluting with AcOEt–hexane to give 2h. Yield:
627 mg (87%). 1H NMR (300 MHz, CDCl3, r.t.) d = 7.38 (dd, 2 H,
J = 5.8, 3.3 Hz), 7.59 (d, 2 H, J = 8.3 Hz), 7.63 (dd, 2 H, J = 5.8,
3.3 Hz), 7.81 (dd, 2 H, J = 8.3, 2.5 Hz), 8.68 (d, 2 H, J = 2.5 Hz). 13C
NMR (75.7 MHz, CDCl3, r.t.): d 88.8, 92.1, 120.1, 125.1, 128.6,
4.10. Typical procedure of the ligand displacement reaction of 1d
In an NMR tube was charged a dmso-d6 (0.60 mL) solution of
1d (4.2 mg, 6.0 ꢂ 10ꢀ3 mmol), the dinitrogen ligand (6.0 ꢂ
10ꢀ3 mmol) and 1,2-diphenylethane (1.1 mg, 6.0 ꢂ 10ꢀ3 mmol,
Internal standard). 1H NMR spectra (r.t.) were checked occasion-
ally. The reactions were monitored by integration of the 1H NMR
signal of 2d.
129.0, 132.2, 138.9, 141.7, 151.2. IR (KBr disk, r.t.)
m 3030, 2223
(C„C), 1456, 1003, 750 cmꢀ1. MS (ESI pos): m/z = 460.9 ([M+Na]+).

174
M. Jung et al. / Polyhedron 40 (2012) 168–174
[6] (a) D. Takeuchi, J. Am. Chem. Soc. 133 (2011) 11106;
4.11. X-ray crystallography
(b) S. Park, T. Okada, D. Takeuchi, K. Osakada, Chem. Eur. J. 16 (2010) 8662;
(c) T. Okada, S. Park, D. Takeuchi, K. Osakada, Angew. Chem., Int. Ed. 46 (2007)
6141;
(d) D. Takeuchi, R. Matsuura, S. Park, K. Osakada, J. Am. Chem. Soc. 129 (2007)
7002;
Crystals of 2a, 1f and 1g suitable for X-ray diffraction study
were obtained by recrystallization from CH2Cl2/hexane, CH2Cl2/
MeCN, and CH2Cl2/MeCN, respectively. All measurements were
made on a Rigaku Saturn70 diffractometer using graphite mono-
(e) S. Park, D. Takeuchi, K. Osakada, J. Am. Chem. Soc. 128 (2006) 3510.
[7] D. Takeuchi, Dalton Trans. 39 (2010) 311.
[8] V.C. Gibson, S.K. Spitzmesser, Chem. Rev. 103 (2003) 283.
[9] F.C. Rix, M. Brookhart, P.S. White, J. Am. Chem. Soc. 118 (1996) 4746.
[10] (a) F. Paul, C. Lapinte, Coord. Chem. Rev. 178–180 (1998) 431;
(b) T.L. Stott, M.O. Wolf, Coord. Chem. Rev. 246 (2003) 89;
(c) R.P. Kingsborough, T.M. Swager, Prog. Inorg. Chem. 48 (1999) 123;
(d) M.I. Bruce, P.J. Low, Adv. Organomet. Chem. 50 (2004) 179.
[11] (a) U. Koert, M.M. Harding, J.-M. Lehn, Nature 346 (1990) 339;
(b) J.-M. Lehn, A. Rigault, J. Siegel, J. Harrowfield, B. Chevrier, D. Moras, Proc.
Natl. Acad. Sci. USA 84 (1987) 2565;
chromated Mo Ka radiation. The data were collected at a temper-
ature of ꢀ160 °C to a maximum 2h value of 55o. A total of 720
oscillation images were collected. The structures were solved by
direct methods and refined against all data by full matrix least-
square on F2 using anisotropic displacement parameters for all
non-hydrogen atoms. All hydrogen atoms were included in the
refinement at geometrically ideal positions and refined with a rid-
ing model. A program package CRYSTAL STRUCTURE for Windows [28]
were used for calculations and for generating the structures.
(c) M. Fujita, Acc. Chem. Res. 32 (1999) 53;
(d) M. Fujita, M. Tominaga, A. Hori, B. Therrien, Acc. Chem. Res. 38 (2005) 371.
[12] (a) T. Taira, Y. Suzaki, K. Osakada, Chem. Eur. J. 16 (2010) 6518;
(b) T. Taira, Y. Suzaki, K. Osakada, Chem. Asian J. 3 (2008) 895;
(c) T. Taira, Y. Suzaki, K. Osakada, Chem. Lett. 37 (2008) 182.
[13] L. Kaganovsky, K.-B. Cho, D. Gelman, Organometallics 27 (2008) 5139.
[14] (a) E. Bosch, C.L. Barnes, Inorg. Chem. 40 (2001) 3097;
(b) N.L. Brennan, C.L. Barnes, E. Bosch, Inorg. Chim. Acta 363 (2010) 3987.
[15] (a) T. Kawano, J. Kuwana, I. Ueda, Bull. Chem. Soc. Jpn. 76 (2003) 789;
(b) T. Kawano, J. Kuwana, T. Shinomaru, C.-X. Du, I. Ueda, Chem. Lett. 30
(2001) 1230;
Acknowledgements
This work was supported by a Grant-in-Aid for Scientific Re-
search for Young Scientists from the Ministry of Education, Culture,
Sports, Science and Technology, Japan (21750058) and by Global
COE Program ‘‘Education and Research Center for Emergence of
New Molecular Chemistry’’. J.M acknowledges scholarship from
Kobayashi International Scholarship Foundation.
(c) E. Bosch, C.L. Barnes, J. Coord. Chem. 56 (2003) 329.
[16] C.L. Barnes, E. Bosch, J. Chem. Cryst. 36 (2006) 563.
[17] J.E. Fiscus, S. Shotwell, R.C. Layland, M.D. Smith, H.-C. zur Loye, U.H.F. Bunz,
Chem. Commun. (2001) 2674.
[18] (a) T. Kawano, T. Shinomaru, I. Ueda, Org. Lett. 4 (2002) 2545;
(b) E. Bosch, C.L. Barnes, N.L. Brennan, G.L. Eakins, B.E. Breyfogle, J. Org. Chem.
73 (2008) 3931;
Appendix A. Supplementary data
(c) S. Shotwell, H.L. Ricks, J.G.M. Morton, M. Laskoski, J. Fiscus, M.D. Smith, K.D.
Shimizu, H.-C. zur Loye, U.H.F. Bunz, J. Organomet. Chem. 671 (2003) 43;
(d) Y.-Z. Hu, C. Chamchoumis, J.S. Grebowicz, R.P. Thummel, Inorg. Chem. 41
(2002) 2296.
CCDC 851271, 851272 and 851273 contains the supplementary
crystallographic data for 1a, 2f and 2g, respectively. These data can
be obtained free of charge via http://www.ccdc.cam.ac.uk/conts/
retrieving.html, or from the Cambridge Crystallographic Data Cen-
tre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: +44 1223-336-
033; or e-mail: deposit@ccdc.cam.ac.uk.
[19] Y. Suzaki, K. Shimada, E. Chihara, T. Saito, Y. Tsuchido, K. Osakada, Org. Lett. 13
(2011) 3774.
[20] A. Mori, M.S.M. Ahmed, A. Sekiguchi, K. Masui, T. Koike, Chem. Lett. 31 (2002)
756.
[21] P. Liao, B.W. Langloss, A.M. Johnson, E.R. Knudsen, F.S. Tham, R.R. Julian, R.J.
Hooley, Chem. Commun. 46 (2010) 4932.
References
[22] (a) P.E. Fanta, Chem. Rev. 64 (1964) 613;
(b) M.F. Semmelhack, Org. React. 19 (1972) 115;
(c) R. Baker, Chem. Rev. 73 (1973) 487.
[1] R.H. Crabtree, D.M.P. Mingos (Eds.), Comprehensive Organometallic Chemistry
III, vol. 8, Elsevier Ltd., 2006.
[23] (a) K. Osakada, R. Sakata, T. Yamamoto, Organometallics 16 (1997) 5354;
(b) K. Osakada, T. Yamamoto, Coord. Chem. Rev. 198 (2000) 379.
[24] (a) T. Yagyu, M. Hamada, K. Osakada, T. Yamamoto, Organometallics 20 (2001)
1087;
(b) T. Yamamoto, S. Wakabayashi, K. Osakada, J. Organomet. Chem. 428 (1992)
223.
[25] D. Drew, J.R. Doyle, Inorg. Synth. 13 (1972) 52.
[26] (a) C.-F. Lin, Y.-H. Lo, M.-C. Hsieh, Y.-H. Chen, J.-J. Wang, M.-J. Wu, Bioorg. Med.
Chem. 13 (2005) 3565;
[2] (a) Y. Suzaki, T. Yagyu, K. Osakada, J. Organomet. Chem. 692 (2007) 326;
(b) Y. Suzaki, K. Osakada, Organometallics 22 (2003) 2193;
(c) Y. Suzaki, K. Osakada, Bull. Chem. Soc. Jpn. 77 (2004) 139.
[3] (a) K. Masui, H. Ikegami, A. Mori, J. Am. Chem. Soc. 126 (2004) 5074;
(b) K. Kobayashi, A. Sugie, M. Takahashi, K. Masui, A. Mori, Org. Lett. 7 (2005)
5083;
(c) A. Sugie, H. Furukawa, Y. Suzaki, K. Osakada, M. Akita, D. Monguchi, A.
Mori, Bull. Chem. Soc. Jpn. 82 (2009) 555.
(b) Q. Zhou, P.J. Carroll, T.M. Swager, J. Org. Chem. 59 (1994) 1294.
[27] Y. Yamaguchi, S. Kobayashi, S. Miyamura, Y. Okamoto, T. Wakamiya, Y.
Matsubara, Z. Yoshida, Angew. Chem., Int. Ed. 43 (2004) 366.
[28] CRYSTAL STRUCTURE: Crystal analysis package, Rigaku and Rigaku/MSC
(2000–2011).
[4] (a) R.A. Widenhoefer, M.A. DeCarli, J. Am. Chem. Soc. 120 (1998) 3805;
(b) N.S. Perch, P. Kisanga, R.A. Widenhoefer, Organometallics 19 (2000) 2541;
(c) N.S. Perch, R.A. Widenhoefer, J. Am. Chem. Soc. 126 (2004) 6332;
(d) R.A. Widenhoefer, Acc. Chem. Res. 35 (2002) 905.
[5] F. Li, C. Xia, Tetrahedron Lett. 48 (2007) 4845.