Dinuclear palladium-azido complexes containing thiophene derivatives: Reactivity toward organic isocyanides and isothiocyanates

Article abstract of DOI:10.1039/b616901e

Cyclopalladated tetranuclear Pd(ii) complexes, [Pd₂(-Cl) ₂(Y)]₂ (Y = L¹ or L²; H ₂L¹ = di(2-pyridyl)-2,2′-bithiophene; H ₂L² = 5,5″-di(2-pyridyl)-2,2′:5′, 2″-terthiophene), containing two pyridyl-α, α′- disubstituted derivatives of thiophene were prepared. Treating these products with PR₃ and subsequently with NaN₃ produced the dinuclear Pd-azido complexes [(PR₃)₂(N₃)Pd-Y-Pd(N ₃)(PR₃)₂] (Y = L¹ or L²) or a cyclometallated complex [(PR₃)(N₃)Pd-Y′- Pd(N₃)(PR₃)] (Y′ = C,N-L²). Reactions of these Pd-azido complexes with CN-Ar (Ar = 2,6-Me₂C₆H ₃, 2,6-i-Pr₂C₆H₃) or R-NCS (R = i-Pr, Et, allyl) led to the complexes containing end-on carbodiimido groups [(PMe₃)₂(NCN-Ar)Pd-Y-Pd(NCN-Ar)(PMe₃) ₂] or S-coordinated tetrazole-thiolato groups {(PMe₃) ₂[CN₄(R)]S-Pd-Y-Pd-S[CN₄)(R)](PMe ₃)₂}. Interestingly, when treated with elemental sulfur, the carbodiimido complexes transformed into the cyclometallated derivatives, [(PMe₃)(NCN-Ar)Pd-Y′-Pd(NCN-Ar)(PMe₃)] (Y′ = C,N-L¹, C,N-L²). We also report the preparation of linear, thienylene-bridged dinuclear Pd complexes [L₂(N₃)Pd-X(or X′)-Pd(N₃)L₂] (L = PMe₃ or PMe ₂Ph; H₂X = 2,2′-bithiophene or H₂X′ = 2,2′:5′,2″-terthiophene) and their reactivity toward organic isocyanide and isothiocyanates. The Royal Society of Chemistry.

Full text of DOI:10.1039/b616901e

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Dinuclear palladium–azido complexes containing thiophene derivatives:
reactivity toward organic isocyanides and isothiocyanates†
Xiaohong Chang,a,b Mi-Young Kim,a Yong-Joo Kim,*a Hyun Sue Huhc and Soon W. Leec
Received 21st November 2006, Accepted 8th January 2007
First published as an Advance Article on the web 18th January 2007
DOI: 10.1039/b616901e
Cyclopalladated tetranuclear Pd(II) complexes, [Pd2(l-Cl)2(Y)]2 (Y = L1 or L2; H2L1 = di(2-pyridyl)-2,
ꢀ
2ꢀ-bithiophene; H2L2 = 5,5ꢀꢀ-di(2-pyridyl)-2,2ꢀ:5ꢀ,2ꢀꢀ-terthiophene), containing two pyridyl-a, a -disub-
stituted derivatives of thiophene were prepared. Treating these products with PR3 and subsequently with
NaN3 produced the dinuclear Pd–azido complexes [(PR3)2(N3)Pd–Y–Pd(N3)(PR3)2] (Y = L1 or L2) or a
cyclometallated complex [(PR3)(N3)Pd–Yꢀ–Pd(N3)(PR3)] (Yꢀ = C,N-L2). Reactions of these Pd–azido
complexes with CN–Ar (Ar = 2,6-Me2C6H3, 2,6-i-Pr2C6H3) or R–NCS (R = i-Pr, Et, allyl) led to the
= =
= =
complexes containing end-on carbodiimido groups [(PMe3)2(N C N–Ar)Pd–Y–Pd(N C N–Ar)-
(PMe3)2] or S-coordinated tetrazole-thiolato groups {(PMe3)2[CN4(R)]S–Pd–Y–Pd–S[CN4)(R)]-
(PMe3)2}. Interestingly, when treated with elemental sulfur, the carbodiimido complexes transformed
ꢀ
ꢀ
= =
= =
into the cyclometallated derivatives, [(PMe3)(N C N–Ar)Pd–Y –Pd(N C N–Ar)(PMe3)] (Y = C,
N-L1, C,N-L2). We also report the preparation of linear, thienylene-bridged dinuclear Pd complexes
[L2(N3)Pd–X(or Xꢀ)–Pd(N3)L2] (L = PMe3 or PMe2Ph; H2X = 2,2ꢀ-bithiophene or H2Xꢀ = 2,2ꢀ:5ꢀ,
2ꢀꢀ-terthiophene) and their reactivity toward organic isocyanide and isothiocyanates.
because the azido ligand may undergo thermal or nucleophilic
Introduction
cycloaddition or imido-compound formation with unsaturated
organic molecules. While the cyclometallated Pd and Pt com-
plexes containing phenyl pyridyl derivatives as C,N-donor ligands
are now relatively common, those containing thienyl pyridyl
derivatives are rare.9–12,14 Moreover, dinuclear azido complexes
containing pyridyl thiophene units of type I (C,N-coordinated)
or type IV (non-cyclometallated or r-bonded thienyl derivatives)
have not been reported yet.
In this work, we describe the preparation and properties of
the dinuclear Pd(II)–azido complexes bridged by pyridyl thio-
phene derivatives, [(PR3)2Pd(N3)–Y–Pd(N3)(PR3)2], in which “Y”
denotes a di(2-pyridyl) bithienyl (L1) or terthienyl ligand (L2)
acting as a C,N-donor chelate ligand (type I) or just a C-donor
ligand (type IV), along with their interconversion between a
cyclometallated and non-cyclometallated form (Scheme 1).
p-Conjugated thiophene compounds have been intensively studied
because of their intriguing electronic or optical properties.1–6
In particular, pyridine-substituted thiophene (thienyl pyridine)
compounds with extended p-electron bonds have been focused
on because of their potential use in the construction of molecular
wires, electronic, or chemical devices.7,8 For transition metal com-
plexes containing a 2-(2ꢀ-thienyl)pyridine unit, four coordination
types (I–IV in Chart 1), chelate (C,N) or monodentate, are
observed. For example, cyclometallated or non-cyclometallated
(r-bond) Pd, Pt, Ru, and Au complexes containing this type of
ligand are known.9–12
Chart 1
We have recently reported the preparation of cyclometallated
Pd(II) complexes containing C,N- or C,N,N-donor ligands such
as 2-phenylpyridyl or 6-phenyl-2,2ꢀ-bipyridyl.13 In that study,
we introduced the azido group to the cyclometallated system,
Scheme 1
aDepartment of Chemistry, Kangnung National University, Kangnung, 210-
702, Korea. E-mail: yjkim@kangnung.ac.kr; Fax: Int + 82 + 33-647-1183;
Tel: Int + 82 + 33-640-2308
bDepartment of Chemistry, Liaoning University, Shenyang, 110036, PR
China
cDepartment of Chemistry, Sungkyunkwan University, Natural Science
Campus, Suwon, 440-746, Korea
† Electronic supplementary information (ESI) available: NMR data. See
DOI: 10.1039/b616901e
Chart 2
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As a comparative work, we also prepared the dinuclear
Pd(II)–azido complexes by empolying linear thienylene ligands,
[(PR3)2Pd(N3)–X(or Xꢀ)–Pd(N3)(PR3)2] (X = bth-C5,C5ꢀ or Xꢀ =
tth-C5,C5ꢀ), and examined their reactivity toward organic iso-
cyanides or isothiocyanates.
Scheme 3
Synthesis of dinuclear Pd–azido complexes containing
pyridyl-a,aꢀ-disubstituted derivatives of thiophene
Cyclopalladated tetranuclear Pd complexes (1 and 2) containing
ꢀ
two pyridyl-a,a -disubstituted derivatives of thiophene (L1 and L2),
Chart 3
which are the starting materials for the corresponding dinuclear
chlorides or azides, were prepared from H2L1 or H2L2 and
Na2PdCl4 (Scheme 4).
The products are slightly soluble in common organic solvents.
Addition of excess PR3 (8 equiv.) to the tetranuclear chloro-
bridged Pd complexes 1 and 2 cleaved the Cl–Pd–Cl bridges to
give the dinuclear Pd chlorides (3, 4, and 7) containing a single
bridging L1 or L2 (Y), and then metathesis with NaN3 gave the
dinuclear Pd–azido complexes, [(PR3)2(N3)Pd–Y–Pd(N3)(PR3)2]
(5, 6, and 8), as shown in Scheme 5.
On the other hand, treating complex 2 with 4 equiv. of PR3
produced a cyclometallated Pd chloride (9) with the thiophene
derivative, a C,N-coordinated L2 (C,N-L2). Subsequent treatment
of 9 with NaN3 produced another cyclometallated Pd–azido
complex (10).
The IR spectra of these complexes display a strong N3
absorption band at 2036–2037 cm−1. Crystallographic data of
5 are given in Table 1. Despite severe disorder of the PMe3
ligand, the ORTEP36 drawing of 5 (Fig. 1) clearly exhibits the
geometry of the dinuclear Pd–azido complex bridged by L1. The
coordination sphere of each Pd can be described as square planar.
The crystallographic inversion center is located in the middle of
the central C–C bond joining two thiophene rings, which explains
why the crystal of complex 5 has the Z value of 4 instead of 8.
Several cyclometallated complexes containing terthienyl-based
ligands and dinuclear complexes bridged by polythiophene or
Results and discussion
Synthesis of pyridyl-a,aꢀ-disubstituted derivatives of thiophene
ꢀ
For the preparation of pyridyl-a,a -disubstituted derivatives of
thiophene (H2L1 and H2L2), we first synthesized halo-a,a -
ꢀ
disubstituted derivatives of thiophene by employing NBS or
AlCl3(cat.)–SO2Cl2 (Scheme 2).15–17 In the subsequent step, the
pyridyl groups were introduced to the a positions of the thiophene
by the Pd-catalyzed Stille coupling reactions (Scheme 3).18–19 The
reactions yielded a mixture of a disubstituted thiophene (major)
and a monosubstituted thiophene (minor), which could be readily
separated by column chromatography.
Scheme 2
Scheme 4
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Table 1 X-Ray data collection and structure refinement for 5, 15 and 26
5
15
26·2CH2Cl2
Formula
FW
C30H46N8P4Pd2S2
919.55
293(2)
0.24 × 0.18 × 0.12
Monoclinic
C2/c
28.363(4)
11.025(1)
15.054(3)
—
98.08(1)
—
4660(1)
4
1.310
1.026
C50H62N6P2Pd2S2
1085.92
293(2)
0.46 × 0.24 × 0.24
Orthorhombic
Pbca
39.276(8)
8.758(2)
14.875(3)
—
—
—
5117(2)
4
0.410
C40H62Cl4N4P4Pd2S2
1141.54
293(2)
0.24 × 0.20 × 0.20
Triclinic
P-1
8.5056(17)
12.325(2)
13.107(4)
87.887(17)
76.69(2)
81.063(16)
1320.9(5)
1
Temperature/K
Crystal size/mm3
Crystal system
Space group
˚
a/A
˚
b/A
˚
c/A
a/◦
b/◦
c /◦
3
˚
V/A
Z
d
cal/g cm−3
1.435
1.114
l/mm−1
0.886
F(000)
1864
2232
582
0.4721
0.8289
x
Tmin
0.6863
0.9102
x
0.4390
0.4970
x
Tmax
Scan type
No. of reflns measured
No. of reflns unique
No. of reflns with I > 2r(I)
4109
4025
2884
194
4485
4485
3323
281
4962
4624
3598
255
No. of parameters refined
−3
˚
Max., in Dq/e A
0.987
0.372
0.666
−3
˚
Min., in Dq/e A
−0.606
−0.824
−0.772
GOF on F2
R
1.025
1.003
1.019
0.0697
0.1747
0.0389
0.0917
0.0463
0.1135
wR2a
a wR2 = R[w(Fo2–Fc2)2]/R[w(Fo2)2]1
Fig. 1 ORTEP drawing36 of compound 5 with 50% probability thermal
◦
˚
ellipsoids. Selected bond lengths (A) and angles ( ): Pd1–C3 2.019(8),
Pd1–N2 2.093(9), Pd1–P2 2.293(3), Pd1–P1 2.319(3), N2–N3 1.11(1),
N3–N4 1.09(1); C3–Pd1–N2 175.7(4), C3–Pd1–P2 89.4(2), N2–Pd1–P2
88.2(3), C3–Pd1–P1 89.4(2), N2–Pd1–P1 93.0(3), P2–Pd1–P1 177.4(1),
C1–S1–C4 90.8(4), N3–N2–Pd1 138.2(9), N4–N3–N2 174(2).
Reactivity towards organic isocyanide
Scheme 5
We recently reported that treatments of late transition-metal–
azides with organic isocyanides gave C-coordinated tetrazolato
or carbodiimido compounds, depending on the nature of the
isocyanides used.28 On the basis of these results, we decided to
employ the same synthetic strategy to prepare novel complexes.
Reactions of the dinuclear Pd–azido complexes 5 and 8 with
CN–Ar (Ar = 2,6-Me2C6H3, 2,6-i-Pr2C6H3) afforded the dinuclear
phosphinothiophene ligands were reported.20–27 However, exam-
ples of the complexes containing pyridyl-substituted thiophene
derivatives are quite rare.9 Furthermore, the reactivity of these
complexes toward organic isocyanide and isothiocyanates has
never been reported.
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Scheme 6
Pd complexes (11–14) containing end-on carbodiimido ligands in
high yield (Scheme 6). The formation of the products could readily
be monitored by IR spectra, which show the disappearance of an
asymmetric stretching band m(N3) of the starting material and the
appearance of a new strong band at 2115–2147 cm−1 due to the
31
= =
carbodiimido group (N C N) of the products. A singlet in the P
NMR spectra of the complexes strongly supports the formation
of the symmetric dinuclear Pd–carbodiimido complexes.
In contrast, the same reaction of 10 with two or more equiv.
of isocyanide (CN–Ar) gave a mixture of three products whose
NMR spectra indicate the presence of a carbodiimido complex (16,
= =
=
isolated), a new imidoyl complex [(PMe3)(N C N–Ar)(–C N–
ꢀ
ꢀ
2
=
= =
Ar)Pd–Y –Pd(–C N–Ar)(N C N–Ar)(PMe3)] (Y = C,N-L ,
Ar = C6H3-2,6-i-Pr2), and an unidentified compound. Several
attempts to separate the mixture were unsuccessful.
Fig. 2 ORTEP drawing of compound 15 with 50% probability thermal
◦
˚
ellipsoids. Selected bond lengths (A) and angles ( ): Pd1–C1 1.995(4),
Pd1–N2 2.078(3), Pd1–N1 2.122(3), Pd1–P1 2.224(1), N2–C10 1.155(5),
N3–C10 1.253(6), N3–C11 1.408(6), C3–C3#1 1.450(7); C1–Pd1–N2
171.7(2), C1–Pd1–N1 81.4(1), N2–Pd1–N1 90.5(1), C1–Pd1–P1 93.1(1),
N2–Pd1–P1 95.0(1), N1–Pd1–P1, 174.3(1), C10–N2–Pd1, 135.9(3),
C10–N3–C11 128.6(4), N2–C10–N3 171.4(5).
However, when treated with elemental sulfur (slight excess) at
room temperature, the dinuclear Pd–carbodiimido complexes 12
and 14 slowly transformed into the dinuclear Pd–carbodiimido
complexes containing C,N-L1 (15) or C,N-L2 (16), which is ac-
companied by dissociation of one PMe3 from each Pd (Scheme 7).
On addition of a slight excess of PMe3, complexes 15 and 16
go back to the starting materials, which indicates a hemilabile
character of the ligands C,N-L1 and C,N-L2.
ligands are C, N or r-donors, and investigated their reactivity
toward isocyanides.13 In the present work, we have also obtained
novel Pd–azido complexes containing the C,N-coordinated (C,N-
L2) or C-coordinated (C-L1 and C-L2) pyridyl thiophene deriva-
tives and observed their transformation to the corresponding car-
bodiimido complexes. The addition of elemental sulfur to the Pd
complexes possessing C,N-donor ligands may be a useful synthetic
strategy for the preparation of other interesting cyclometallated
Pd compounds.
The formation of the cyclometallated Pd–carbodiimido com-
1
plexes can be readily followed by H NMR, which exhibits the
appearance of a doublet due to one PMe3 ligand per Pd in the
products. The molecular structure of orange-red complex 15 was
determined by X-ray diffraction. The dinuclear Pd complex 15
(Fig. 2) can be regarded as having two equal halves, each of which
consists of one half of C,N-L1, a carbodiimido group, and a PMe3
ligand in a square-planar geometry. The molecule lies about an
inversion center, which is at the midpoint of the C–C bond linking
the two thiophene moieties.
Reactions toward organic isothiocyanates
Recently, we prepared the cyclometallated Pd–azido complexes
[Pd(N3)(PR3)L] (L = 2-phenylpyridine derivatives), in which the
We have previously reported on the dipolar cycloaddition of
organic isothiocyanates (R–NCS) to a transition-metal–azido
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Scheme 7
bond to give S-coordinated tetrazole-thiolato compounds.29 Con-
Synthesis of dinuclear Pd–azido complexes containing linear
sistent with our expectations, such reactivity was also observed
in the reactions of R–NCS with the cyclometallated Pd–azido
complexes containing thienylpyridine derivatives. Treating 5 and 8
with R–NCS (R = i-Pr, ethyl, allyl) produced tetrazole-thiolato
Pd complexes (17–19), which were presumably formed by the
dipolar cycloaddition of the isothiocyanates to the Pd–azido bond
(Scheme 8).
thiophene derivatives
Dinuclear group 10 metal complexes containing a linear aromatic
array are known and have been prepared by double oxidative
addition of dihalo aromatic compounds to zerovalent metal
complexes.30–33 However, examples containing a heteroaromatic
array such as thiophene are rare.22–24 These complexes are useful
Scheme 8
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for the construction of self-assembled macromolecules or as
potential building blocks for electronic or optical molecules.23 For
a comparative study of cyclometallated and non-cyclometallated
(r-bonded) dinuclear Pd–azido complexes with linear thiophene
derivatives, we decided to synthesize the dinuclear Pd–azido
complexes containing these derivatives.
Pt(II) complexes which result from the isocyanide insertion into
Pt–C bonds.22 We have also observed similar reactvities for
the thienylene-bridged Pd(II) halides.24 In this context, we have
investigated the reactivity of the thienylene-bridged Pd–azido
compounds toward organic isocyanides and isothiocyanates.
Treating bithienylene- or terthienylene-bridged Pd–azido com-
plexes with aromatic isocyanides (CN–Ar) at room temperature
produced p-bond-extended Pd complexes containing end-on car-
bodiimido groups (Scheme 10).
Reactions of Pd(CH2 CHPh)L2 (L = PMe3 or PMe2Ph),34
=
which could be generated in situ from trans-PdEt2L2 and styrene,
with a dihalo thiophene (5,5ꢀ-dichloro-2,2ꢀ-bithiophene (H2bth) or
5,5ꢀꢀ-dichloro-2,2ꢀ:5ꢀ,2ꢀꢀ-terthiophene (H2tth)) in a 2 : 1 molar ratio
gave the double oxidative addition products [L2(Cl)Pd–X(or Xꢀ)–
Pd(Cl)L2] (X = bth-C5,C5ꢀ or Xꢀ = tth-C5,C5ꢀꢀ) (20–22) (Scheme 9).
The subsequent treatment of complexes 20–22 with excess NaN3
produced the corresponding Pd–azido complexes [L2(N3)Pd–
X(or Xꢀ)–Pd(N3)L2] (23–25). In contrast, such reactivity was
not observed for the bromo analogue [L2(Br)Pd–X–Pd(Br)L2],
probably because of the comparable nucleophilicity of the N3
and Br groups. A singlet in the 31P NMR data of the complexes
supports the symmetric structure of complexes 23–25. It is worth
noting that these reactions do not proceed via cyclometallation
that would result in the S,C-coordination of the thiophene moiety.
Scheme 10
The formation of products could be readily confirmed by the
IR spectrum, which shows the disappearance of an asymmetric
N3 stretching band of the starting material and the appearance
−1
= =
of a new strong N C N band at 2140 (for 26) or 2131 cm
(for 27) in the product. The spectral data indicate that the imido
=
(C N–R) compound, formed by the isocyanide insertion into the
Pd–C (thiophene ring), does not exist. The molecular structure
of a yellow crystalline complex 26 was determined by X-ray
crystallography (Fig. 3). The molecule lies around an inversion
center, which is at the midpoint of the C–C bond linking the
two thiophene moieties. The coordination sphere of Pd can be
described as square planar. Two sulfur atoms are oriented in a trans
manner in the thiophene rings, which link two [Pd(PMe3)2(NCN–
C6H3-2,6-Me2)] moieties to give a rod-shaped compound. The
molecular plane, defined by Pd1, P1, P2, C1, and N1, is essentially
Scheme 9
Reactivity toward organic isocyanides and isothiocyanates
˚
planar with an average atomic displacement of 0.0297 A, to which
Sonogashira and co-workers reported that the thienylene-bridged
Pt(II) halides reacted with organic isocyanides to give dinuclear
the thiophenyl ring is roughly perpendicular with a dihedral angle
of 84.0 (1)◦.
◦
˚
Fig. 3 ORTEP drawing of compound 26 with 50% probability thermal ellipsoids. Selected bond lengths (A) and angles ( ): atoms flagged with
a superscript letter “a” are at equivalent position (1 − x, 1 − y, 1 − z): Pd1–C1 1.992(4), Pd1–N1 2.053(5), Pd1–P2 2.3111(15), Pd1–P1 2.3113(15),
N1–C5 1.155(6), N2–C5 1.258(), N2–C6 1.387(7); N1–Pd1–P2 91.37(16), C1–Pd1–P1 88.50(14), N1–Pd1–P1 92.37(16), P2–Pd1–P1 175.11(6), N1–C5–N2
171.9(7).
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The dinuclear Pd–azide compound 23 also underwent cy-
cloaddition with R–NCS (R = ethyl, allyl) to give dinuclar
Pd compounds with S-coordinated heterocycles as shown in
Scheme 11.
Synthesis of pyridyl-a,aꢀ-disubstituted derivatives of thiophene:
5,5ꢀ-di(2-pyridyl)-2,2ꢀ-bithiophene (H2L1) and 5,5ꢀꢀ-di(2-pyridyl)-
2,2ꢀ:5ꢀ,2ꢀꢀ-terthiophene (H2L2). A mixture of 5,5ꢀ-dibromo-2,2ꢀ-
bithiophene (0.609 g, 1.88 mmol), (2-pyridyl)-tri-n-butylstannane
(1.73 g, 4.7 mmol), Pd(PPh3)2Cl2 (0.106 g, 0.15 mmol), and LiCl
(0.797 g, 18.80 mmol) in toluene (60 cm3) was refluxed for 2 days.
After cooling to room temperature, a saturated KF (20 cm3)
solution was added, and the mixture was stirred for 30 min.
A large amount of CH2Cl2 was added to the mixture, and the
solid residue was filtered off. 5% NaHCO3 (150 cm3) solution was
added to the filtrate. Distilled water was added to the separated
organic phase, and the organic phase was separated and dried over
anhydrous Na2SO4. After the solvent was completely evaporated,
the yellow solids were obtained. The crude product was purified
by chromatography (silica gel, CHCl3) to give a yellow solid
product (0.374 g, 62%). H2L1: ESI-MS: m/z = 321.0603 (MH+)
for C18H12N2S2. M = 320.4334; dH (CDCl3): 7.15 (2 H, dd, J =
1.7, 6.8 Hz), 7.26 (2 H, d, J = 3.8 Hz), 7.49 (2 H, d, J = 3.8 Hz),
7.63–7.72 (4 H, m), 8.57 (2 H, m).
Scheme 11
In summary, we prepared the novel dinuclear Pd(II)–azido
H2L1 could also be prepared by treating pyridyl thiophene with
n-BuLi and then CuCl2/O2.9
complexes bridged by
a pyridyl thiophene derivative (Y
or Yꢀ), [(PR3)2(N3)Pd–Y–Pd(N3)(PR3)2] and [(PR3)(N3)Pd–Yꢀ–
Pd(N3)(PR3)], in which Y or Yꢀ acts as either a r-donor or
a cyclometallated C,N-donor ligand. These complexes reacted
with organic isocyanides (CN–Ar) and isothiocyanates (SCN–
H2L2 was prepared in a similar manner (0.147 g, 30%). H2L2:
(Found: C, 65.25; H, 3.82; N, 6.55%. ESI-MS: m/z = 403.1425
(MH+). C22H14N2S3 (Mr = 402.5584) requires C, 65.64; H, 3.51;
N, 6.96%); dH (CDCl3): 7.15 (2 H, dd, J = 1.8, 5.0 Hz), 7.17 (2 H,
S), 7.19 (2 H, d, J = 3.8 Hz), 7.49 (2 H, d, J = 4.0 Hz), 7.64–7.70
(4 H, m), 8.57 (2 H, m). 13C NMR spectrum could not be obtained
due to the compound’s poor solubility.
= =
R) to give p-bond-extended Pd complexes, [(PR3)2(N C N–
= =
Ar)Pd–Y–Pd(N C N–Ar)(PR3)2] containing end-on carbodi-
imido groups and dinuclear Pd complexes with S-coordinated
heterocycle rings [(PR3)2(SCN4R)Pd–Y–Pd(SCN4R)(PR3)2], re-
spectively. Non-cyclometallated (r-bond) forms are converted to
the cyclometallated (C,N) forms and vice versa on addition of
elemental sulfur or PR3, which indicates the hemilabile character
of the pyridyl thiophene ligands. Finally, we prepared dinuclear
Pd–azido complexes with linear bithienyl (or terthienyl) ligands,
which reacted with organic isocyanides or isothiocyanates to give
rod-shaped dinuclear Pd compounds.
Preparation of [Pd2(l-Cl)2(C,N-L1)]2 (1) and [Pd2(l-Cl)2(C,N-
L2)]2 (2). Na2PdCl4 (0.300 g, 1.02 mmol) was dissolved in
degassed ethanol (90 cm3) and H2L1 (0.196 g, 0.61 mmol) was
added to the resulting red solution. The yellow suspension slowly
turned to a dark orange suspension. After stirring for 24 h, the dark
orange solids were filtered out with a glass frit and washed with
distilled water and ether. The product was dried under vacuum
to give a dark red solid, complex 1 (0.498 g, 81%). Complex 1:
(Found: C, 36.34; H, 1.92; N, 4.78%. ESI-MS: m/z = 1205.6500
(MH+). C36H20Cl4N4Pd4S4 (Mr = 1204.3284) requires: C, 35.90;
H, 1.67; N, 4.65%); NMR spectra could not be obtained owing to
its poor solubility.
Complex 2 was prepared in a similar way (82%). Complex
2: ESI-MS: m/z = 1369.9897 (MH+). C44H24Cl4N4Pd4S6 (Mr =
1368.5751); dH (DMF-d7): 7.07 (4 H, dd, J = 1.1, 5.0 Hz), 7.21
(4 H, s), 7.21(4 H, d, J = 3.8 Hz), 7.60 (4 H, d, J = 3.8 Hz), 7.64
(4 H, dd, J = 1.8, 7.5 Hz), 8.33–8.35 (4 H, m). 13C NMR spectrum
could not be obtained due to its poor solubility.
Experimental
General, materials and measurements
All manipulations of air-sensitive compounds were performed
under N2 or Ar by standard Schlenk techniques. Solvents were
distilled from Na–benzophenone. The analytical laboratories at
Kangnung National University carried out elemental analyses
using CE instruments EA1110. IR spectra were recorded on a
1
Perkin Elmer BX spectrophotometer. NMR (1H, 13C{ H}, and
1
31P{ H}) spectra were obtained on a JEOL Lamda 300 MHz
spectrometer. Chemical shifts were referenced to internal Me4Si
or to external 85% H3PO4. Mass spectra were obtained at Korea
Basic Science Institute (Seoul) and the analytical laboratories of
Kangnung National University. Complexes trans-PdEt2L2 (L =
PMe3 and PMe2Ph) were prepared by the literature method.34
Cleavage of complexes 1 and 2 by tertiary phosphines (PMe3,
PEt3). To a Schlenk flask containing complex 1 (0.202 g,
0.17 mmol) were added CH2Cl2 (30 cm3) and PMe3 (0.14 cm3,
1.36 mmol) in that order. The red suspension turned to a yellow
homogeneous solution. After stirring for 2 h, the mixture was
evaporated to give orange solids, which were recrystallized from
CH2Cl2–hexane to give orange crystals of [(PMe3)2(Cl)Pd–Y–
Pd(Cl)(PMe3)2] (Y = L1) (3, 0.200 g, 66%). Complex 3: (Found:
C, 40.18; H, 5.33; N, 2.94. C30H46Cl2N2P4Pd2S2 requires: C, 39.75;
H, 5.11; N, 3.09%).
Preparations
Halo-a,aꢀ-disubstituted derivatives of thiophene compounds.
5,5ꢀ-dibromo-2,2ꢀ-bithiophene,
5,5ꢀꢀ-dibromo-2,2ꢀ:5ꢀ,2ꢀꢀ-terthio-
phene, 5,5ꢀ-dichloro-2,2ꢀ-bithiophene, and 5,5ꢀꢀ-dichloro-2,2ꢀ:5ꢀ,2ꢀꢀ-
terthiophene were prepared according to literature methods.15–17
798 | Dalton Trans., 2007, 792–801
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©

View Article Online
Complexes [(PEt3)2(Cl)Pd–Y–Pd(Cl)(PEt3)2] (Y = L1) (4, 39%)
and [(PMe3)2(Cl)Pd–Y–Pd(Cl)(PMe3)2] (Y = L2) (7, 47%) were
prepared in a similar way.
Reaction of [(PMe3)2(N C N–Ar)Pd–Y–Pd(N C N–Ar)-
(PMe3)2] (Y = L1 or L2, Ar = C6H3-2,6-i-Pr2) with elemental
sulfur. CH2Cl2 (5 cm3) and elemental sulfur (0.005 g, 0.15 mmol)
were added sequentially to a Schlenk flask containing 12 (0.074 g,
0.060 mmol). The initial yellow solution slowly turned to an
orange suspension. After stirring for 12 h at room temperature, the
solvent was completely evaporated, and then the resulting residue
was solidified with diethyl ether. The solids were filtered off and
washed with hexanes to give crude solids. Recrystallization from
= =
= =
The orange complex [(PMe3)(Cl)Pd–Yꢀ–Pd(Cl)(PMe3)] (Yꢀ =
C,N-L2) (9, 42%) was prepared from complex 2 and PMe3 in the
mole ratio of 1 : 4.
Complexes 3, 4, 7, and 9 were further treated with NaN3 to pre-
pare the corresponding azido complexes 5, 6, 8, and 10 (see below).
[(PR3)2(N3)Pd–Y–Pd(N3)(PR3)2] (Y = L1, L2; R = Me, Et) (5,
6, 8) and [(PR3)(N3)Pd–Yꢀ–Pd(N3)(PR3)] (Yꢀ = C,N–L2, R = Me)
(10). To a Schlenk flask containing 3 (0.216 g, 0.24 mmol) were
added CH2Cl2 (12 cm3) and NaN3 solution (0.0618 g, 0.96 mmol)
dissolved in H2O (2 cm3) in that order. The initial orange
solution turned to a yellow suspension. After stirring for 18 h
at room temperature, the solvent was completely removed under
vacuum, and the remaining solid was extracted with CH2Cl2.
Recrystallization from CH2Cl2–hexane gave yellow crystals of
[(PMe3)2(N3)Pd–Y–Pd(N3)(PMe3)2] (Y = L1) (5, 0.189 g, 86%).
Complex 5: (Found: C, 38.92; H, 5.26; N, 12.30. C30H46N8P4Pd2S2
requires C, 39.18; H, 5.04; N, 12.18%); mmax/cm−1 (N3): 2036 (vs).
Complexes [(PEt3)2(N3)Pd–Y–Pd(N3)(PEt3)2] (Y = L1) (6,
67%), [(PMe3)2(N3)Pd–Y–Pd(N3)(PMe3)2] (Y = L2) (8, 76%), and
[(PMe3)(N3)Pd–Yꢀ–Pd(N3)(PMe3)] (Yꢀ = C,N-L2) (10, 70%) were
prepared in a similar manner. Complex 6: (Found: C, 46.80; H,
6.72; N, 10.67. C42H70N8P4Pd2S2 requires C, 46.37; H, 6.49; N,
10.30%); mmax/cm−1 (N3): 2037 (vs). Complex 8: (Found: C, 40.99;
H, 4.88; N, 10.83. C34H48N8P4Pd2S3 requires C, 40.77; H, 4.83; N,
11.19%); mmax/cm−1 (N3): 2036 (vs). Complex 10: (Found: C, 39.72;
H, 3.67; N, 12.32. C28H30N8P2Pd2S3 requires C, 39.58; H, 3.56; N,
13.19%); mmax/cm−1 (N3): 2037 (vs).
CH2Cl2–ether gave orange crystals of [(PMe3)(N C N–Ar)Pd–
= =
ꢀ
ꢀ
1
= =
=
Y –Pd(N C N–Ar)(PMe3)] (Y = C,N-L , Ar C6H3-2,6-i-Pr2)
(15, 0.061 g, 93%). Complex 15 (Found: C, 54.89; H, 5.82; N, 7.60.
C50H62N6P2Pd2S2 requires C, 55.30; H, 5.75; N, 7.74%); mmax/cm−1
= =
(N C N): 2098 (vs).
Complex
ꢀ
= =
= =
[(PMe3)(N C N–Ar)Pd–Y –Pd(N C N–Ar)-
2
(PMe3)] (Yꢀ = C,N-L , Ar C6H3-2,6-i-Pr2) (16, 94%) was
prepared in a similar way. Complex 16: (Found: C, 55.18; H, 5.34;
N, 7.11. C54H64N6P2Pd2S3 requires C, 55.52; H, 5.52; N, 7.19%);
=
mmax/cm−1 (N C N): 2138 (vs).
= =
1
2
=
Reactions of [(PMe3)2(N3)Pd–Y–Pd(N3)(PMe3)2] (Y L or L )
= =
(5 and 8) with R–N C S (R = i-Pr, Et or allyl). To a Schlenk
flask containing 5 (0.081 g, 0.088 mmol) were added CH2Cl2
(5 cm3) and isopropyl isothiocyanate (0.031 cm3, 0.35 mmol)
in that order. After stirring for 20 h at room temperature, the
solvent was completely removed, and then the resulting residue
was solidified with hexane. The solids were filtered off and washed
with hexane (3 cm3 × 2) to give crude solids. Recrystallization from
CH2Cl2–hexane gave yellow solids of [(PMe3)2(SCN4-i-Pr)Pd–Y–
Pd(SCN4-i-Pr)(PMe3)2] (Y = L1) (17, 0.090 g, 90%). Complex 17:
(Found: C, 40.99; H, 5.61; N, 12.24. C38H60N10P4Pd2S4 requires C,
40.68; H, 5.39; N, 12.48%).
Complexes [(PMe3)2(SCN4–Et)Pd–Y–Pd(SCN4–Et)(PMe3)2]
(Y = L1) (18, 90%) and [(PMe3)2(SCN4–R)Pd–Y–Pd(SCN4–
R)(PMe3)2] (Y = L2, R = allyl) (19, 70%) were prepared in a
similar way. Complex 18: (Found: C, 39.68; H, 5.23; N, 12.25.
C36H56N10P4Pd2S4 requires C, 39.53; H, 5.16; N, 12.80%). Complex
19: (Found: C, 41.68; H, 4.92; N, 11.17. C42H58N10P4Pd2S5 requires
C, 42.04; H, 4.87; N, 11.67%).
Reaction of [(PMe3)2(N3)Pd–Y–Pd(N3)(PMe3)2] (Y = L1 or L2)
(5 and 8) with CN–Ar (Ar = C6H3-2,6-Me2 or C6H3-2,6-i-Pr2).
CH2Cl2 (6 cm3) and 2,6-dimethylphenyl isocyanide (0.022 g,
0.17 mmol) were added sequentially to a Schlenk flask containing
5 (0.070 g, 0.076 mmol). The initial yellow solution slowly turned
to a yellowish green solution. After stirring for 4 h at room
temperature, the solvent was completely removed, and then the
resulting residue was solidified with hexane. The solids were
filtered and washed with hexanes to give crude solids, which were
recrystallized from CH2Cl2–hexane to give dark yellow crystals
Preperation of [(PMe3)2(Cl)Pd–X–Pd(Cl)(PMe3)2] (X = bth-
C5,C5ꢀꢀ) (H2bth = 2,2ꢀ-bithiophene) (20) and [(PR3)2(Cl)Pd–Xꢀ–
Pd(Cl)(PR3)2] (Xꢀ = tth-C5,C5ꢀ) (H2tth = 2,2ꢀ:5ꢀ,2ꢀ-terthiophene)
(R = Me (21), Me2Ph (22)). To a Schlenk flask containing
trans-PdEt2(PMe3)2 (0.336 g, 1.06 mmol) at 0 were added styrene
(0.441 g, 4.24 mmol) and THF (3 cm3) sequentially. The mixture
was heated at 55 ◦C for 30 min to give a yellow solution. At room
temperature 5,5ꢀ-dichloro-2,2ꢀ-bithiophene (0.122 g, 0.52 mmol)
was added to the mixture, and the yellow solution turned to a pale
yellow suspension. After stirring for 2 h at room temperature,
the solvent was completely removed under vacuum, and then
the resulting residue was solidified with hexane. The solids were
filtered and washed with hexane (3 cm3 × 2) to give crude
solids. Recrystallization from CH2Cl2–hexane gave gray solids of
[(PMe3)2(Cl)Pd–X–Pd(Cl)(PMe3)2] (X = bth-C5,C5ꢀ) (20, 0.380 g,
80%). Complex 20: (Found: C, 32.06; H, 5.56. C20H40Cl2P4Pd2S2
requires C, 31.93; H, 5.36%).
= =
= =
of [(PMe3)2(N C N–Ar)Pd–Y–Pd(N C N–Ar)(PMe3)2] (Y =
L1, Ar = C6H3-2,6-Me2) (11, 0.067 g, 77%). Complex 11: (Found:
C, 50.93; H, 5.86; N, 7.04. C48H64N6P4Pd2S2 requires C, 51.20; H,
5.73; N, 7.46%); mmax/cm−1 (N C N): 2147 (vs).
Complexes [(PMe3)2(N C N–Ar)Pd–Y–Pd(N C N–Ar)-
= =
= =
= =
(PMe3)2] (Y
=
L1, Ar
=
C6H3-2,6-i-Pr2) (12, 75%),
= =
2
= =
[(PMe3)2(N C N–Ar)Pd–Y–Pd(N C N–Ar)(PMe3)2] (Y = L ,
= =
Ar = C6H3-2,6-Me2) (13, 95%) and [(PMe3)2(N C N–Ar)Pd–
2
= =
Y–Pd(N C N–Ar)(PMe3)2] (Y = L , Ar = C6H3-2,6-i-Pr2) (14,
80%) were prepared in a similar way. Complex 12: (Found: C,
54.69; H, 6.82; N, 6.61. C56H80N6P4Pd2S2 requires C, 54.32; H,
6.51; N, 6.79%); mmax/cm−1 (N C N): 2129 (vs). Complex 13;
= =
(Found: C, 51.34; H, 5.62; N, 6.71. C52H66N6P4Pd2S3 requires
C, 51.70; H, 5.51; N, 6.96%); mmax/cm−1 (N C N): 2137 (vs).
= =
Complex 14: (Found: C, 54.17; H, 6.41; N, 6.05. C60H82N6P4Pd2S3
Complexes [(PMe3)2(Cl)Pd–Xꢀ–Pd(Cl)(PMe3)2] (Xꢀ
=
tth-
requires C, 54.58; H, 6.26; N, 6.37%); mmax/cm−1 (N C N): 2115
(vs).
C5,C5ꢀꢀ) (21, 45%) and [(PMe2Ph)2(Cl)Pd–Xꢀ–Pd(Cl)(PMe2Ph)2]
(Xꢀ = tth-C5,C5ꢀꢀ) (22, 40%) were prepared in a similar way.
= =
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Complex 21: (Found: C, 34.83; H, 5.21. C24H42Cl2P4Pd2S3 requires
C, 34.55; H, 5.07%). Complex 22: (Found: C, 48.78; H, 4.53.
C44H50Cl2P4Pd2S3 requires C, 48.81; H, 4.65%).
Complex 29: (Found: C, 33.03; H, 5.11; N, 11.54. C26H50N8P4Pd2S4
requires C, 33.23; H, 5.36; N, 11.92%).
Complexes 20–22 were treated further with NaN3 to produce
the corresponding azido complexes 23–25 (see below).
X-Ray structure determination
X-Ray data of complexes 5, 15, and 26 were collected with
a Siemens P4 diffractometer equipped with a Mo X-ray tube.
Intensity data were corrected for absorption with W-scan data.
All calculations were carried out with the SHELX-97 programs.35
All the structures were solved by direct methods. All hydrogen
atoms were generated in ideal positions and refined in a riding
model and all non-hydrogen atoms were refined anisotropically,
except the carbon atoms (C13–C15) in one phosphine ligand
of complex 5, which were extremely disordered and therefore
refined isotropically. Details of crystal data, intensity collection,
and refinement details are given in Table 1.
Preparation of [(PMe3)2(N3)Pd–X–Pd(N3)(PMe3)2] (X = bth-
C5,C5ꢀ; H2bth = 2,2ꢀ-bithiophene) (23) and [(PR3)2(N3)Pd–Xꢀ–
Pd(N3)(PR3)2] (Xꢀ = tth-C5,C5ꢀꢀ; H2tth = 2,2ꢀ:5ꢀ,2ꢀꢀ-terthiophene;
R = Me (24), Me2Ph (25)). To a Schlenk flask containing 20
(0.281 g, 0.37 mmol) were added CH2Cl2 (15 cm3) and NaN3
solution (0.073 g, 1.11 mmol) dissolved in H2O (2 cm3) in that
order. The initial yellow solution turned to a yellow suspension.
After stirring for 11 h at room temperature, the solvent was
completely evaporated to give pale yellow solids, which were
extracted with CH2Cl2. Recrystallization from CH2Cl2–hexane
gave pale yellow solids of complex 23 (0.221 g, 77%). Complex
23: (Found: C, 31.36; H, 5.45, N, 10.37. C20H40N6P4Pd2S2 requires
C, 31.38; H, 5.27; N, 10.98%); mmax/cm−1 (N3): 2032 (vs).
CCDC reference numbers 628104–628106. For crystallographic
data in CIF or other electronic format see DOI: 10.1039/b616901e
Complexes [(PMe3)2(N3)Pd–Xꢀ–Pd(N3)(PMe3)2] (Xꢀ = tth-
C5,C5ꢀꢀ) (24, 73%) and [(PMe2Ph)2(N3)Pd–Xꢀ–Pd(N3)(PMe2Ph)2]
(Xꢀ = tth-C5,C5ꢀꢀ) (25, 98%) were prepared in a similar way.
Complex 24: (Found: C, 34.21; H, 5.32; N, 9.63. C24H42N6P4Pd2S3
requires C, 34.01; H, 4.99; N, 9.92%); mmax/cm−1 (N3): 2036 (vs).
Complex 25: (Found: C, 48.38; H, 4.85; N, 7.26. C44H50N6P4Pd2S3
requires C, 48.23; H, 4.60; N, 7.67); mmax/cm−1 (N3): 2037.
Acknowledgements
This work was supported by Grant R05-2004-000-10149-0 from
the Korea Research Foundation and partly from the NURI-2004-
0244 and 2006-006 of Gangwon Advanced Materials
References
Reaction of [(PMe3)2(N3)Pd–X–Pd(N3)(PMe3)2] (X = bth-
C5,C5ꢀ) (23) with CN–Ar (Ar = C6H3-2,6-Me2 or C6H3-2,6-i-Pr2).
To a Schlenk flask containing 23 (0.094 g, 0.12 mmol) were added
sequentially CH2Cl2 (10 ml) and 2,6-dimethylphenyl isocyanide
(0.034 g, 0.25 mmol). After the yellow solution was stirred for
4 h at room temperature, the solvent was removed, and then the
resultingresidue was solidified with hexane. The solids were filtered
off and washed with hexanes to give crude solids. Recrystallization
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= =
from CH2Cl2–hexane gave yellow crystals of [(PMe3)2(N C N–
5
5ꢀ
= =
=
Ar)Pd–X–Pd(N C N–Ar)(PMe3)2] (X = bth-C ,C ; Ar C6H3-
2,6-Me2) (26, 0.087 g, 73%). Complex 26: (Found: C, 42.39; H,
5.73; N, 4.70. C40H62N4Cl4P4Pd2S2 requires C, 42.08; H, 5.47; N,
4.91%); mmax/cm−1 (N C N): 2140 (vs).
= =
= =
= =
Complex
[(PMe3)2(N C N–Ar)Pd–X–Pd(N C N–
5
5ꢀ
=
Ar)(PMe3)2] (X = bth-C ,C ; Ar C6H3-2,6-i-Pr2) (27, 48%)
was prepared in a similar way. Complex 27: (Found: C, 50.67;
H, 6.64; N, 5.24. C46H74N4P4Pd2S2 requires C, 50.97; H, 6.88; N,
5.17%); mmax/cm−1 (N C N): 2131 (vs).
= =
12 M. V. Kulikova, P.-I. Kvam, J. Songstad and K. P. Balashev, Russ. J. Gen.
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Reaction of [(PMe3)2(N3)Pd–X–Pd(N3)(PMe3)2] (X = bth-
5
5ꢀ
= =
C ,C ) (23) with R–N C S (R = allyl or Et). To a Schlenk flask
containing 23 (0.101 g, 0.13 mmol) were added CH2Cl2 (8 ml) and
allyl isothiocyanate (0.027 cm3, 0.27 mmol) in that order. After
stirring for 14 h at room temperature, the solvent was removed,
and the resulting residue was solidified with hexane. The solids
were filtered and washed with hexane (3 cm3 × 2) to give crude
solids. Recrystallization from CH2Cl2–hexane gave yellow solids of
[(PMe3)2(SCN4–R)Pd–X–Pd(SCN4–R)(PMe3)2] (X = bth-C5,C5ꢀ;
R = allyl) (28, 0.079 g, 62%). Complex 28: (Found: C, 35.03; H,
5.10; N, 11.46. C28H50N8P4Pd2S4 requires C, 34.89; H, 5.23; N,
11.63%).
15 G. Zotti, G. Schiavon, A. Berlin and G. Pagani, Chem. Mater., 1993, 5,
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[(PMe3)2(SCN4–Et)Pd–X–Pd(SCN4–Et)(PMe3)2]
(X = bth-C5,C5ꢀ) (29, 88%) was prepared in a similar way.
800 | Dalton Trans., 2007, 792–801
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The Royal Society of Chemistry 2007
©

View Article Online
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