Linear homobimetallic palladium complexes with end-capped SC(O)Me units

Article abstract of DOI:10.1016/j.jorganchem.2008.09.031

Rigid-rod structured homobimetallic palladium complexes of type [{trans-(Me(O)CS-4-C₆H₄-C₆H₄)(Ph₃P)₂Pd}₂(μ-N^∩N)](OTf)₂ (8a, μ-N^∩N = 4,4′-bipyridi

Full text of DOI:10.1016/j.jorganchem.2008.09.031

Journal of Organometallic Chemistry 694 (2009) 27–35
Contents lists available at ScienceDirect
Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Linear homobimetallic palladium complexes with end-capped SC(O)Me units
a
b
a
a
a
Heinrich Lang a, , Katrin Döring , Deeb Taher , Uwe Siegert , Bernhard Walfort , Tobias Rüffer ,
*
Rudolf Holze c
a Technische Universität Chemnitz, Fakultät für Naturwissenschaften, Institut für Chemie, Lehrstuhl für Anorganische Chemie, Straße der Nationen 62, 09111 Chemnitz, Germany
b Tafila Technical University, Department of Chemistry, Tafila, At Tafila 66110, Jordan
c Technische Universität Chemnitz, Institut für Chemie, AG Elektrochemie, 09111 Chemnitz, Germany
a r t i c l e i n f o
a b s t r a c t
Article history:
Rigid-rod structured homobimetallic palladium complexes of type [{trans-(Me(O)CS-4-C6H4-
C6H4)(Ph3P)2Pd}2(
CH-C5H4N; 8c,
l l l
-N\N)](OTf)2 (8a, -N\N = 4,40-bipyridine, bpy; 8b, -N\N = C5H4N-CH@N-N@
Received 18 April 2008
Received in revised form 16 September
2008
l
-N\N = C5H4N-CH@CH-C6H4-CH@CH-C5H4N; 8d, -N\N = C5H4N-CH@N-C6H4-N@CH-
l
C5H4N) were synthesized by the reaction of trans-[(Me(O)CS-4-C6H4-C6H4)(Ph3P)2Pd](OTf) (6) with 0.5
equivalents of N\N (7a, N\N = bpy; 7b, N\N = C5H4N-CH@N-N@CH-C5H4N; 7c, N\N = C5H4N-CH@CH-
C6H4-CH@CH-C5H4N; 7d, N\N = C5H4N-CH@N-C6H4-N@CH-C5H4N) in high yield. Complex 6 was accessi-
ble by the subsequent reaction of I-4-C6H4-C6H4-40-SC(O)Me (2) with [(PPh3)4Pd] (3) to produce
trans-[(I)(Me(O)CS-4-C6H4-C6H4)(Ph3P)2Pd] (4) which further reacted with AgOTf (5) to give 6.
The structures of 4 and 8c in the solid state are reported. Most characteristic for these systems is the
square-planer coordination geometry of palladium with trans-positioned PPh3 groups. This automatically
positions the iodo ligand and the Me(O)CS-4-C6H4-C6H4 unit (complex 4) or the nitrogen donor atoms of
the C5H4N-CH@CH-C6H4-CH@CH-C5H4N connectivity and the thio-acetyl group Me(O)CS-C6H4-C6H4
(complex 8c) trans to each other. In 8c a Pd–Pd separation of 20.156 Å is typical.
Accepted 22 September 2008
Available online 27 September 2008
Keywords:
Palladium
Thiol
Nitrogen Lewis-bases
Oxidative addition
Cyclic voltammetry
The electrochemical redox behavior of 2, 4 and 8 is discussed.
Ó 2008 Elsevier B.V. All rights reserved.
1. Introduction
faces [11]. The separation of the metal atoms from each other
could, for example, be realized by the different size and length of
There is a wide interest in the synthesis of one-dimensional or-
ganic and organometallic compounds because they might be of
considerable use in, for example, the developing field of molecular
electronics [1–4], as conducting wires [5] or as single-molecule
insulators [6,7]. From literature reports it appeared that the prop-
erties of molecular wires strongly depend on the nature of the re-
dox-active termini and the appropriate rigid-rod shaped
connecting spacers [8]. Among them, conjugated end-capped or-
ganic thiols have received a great deal of attention because of their
intrinsic semiconductor [5] or insulator properties [6], and of their
unique capability to form well-ordered monolayers via self-assem-
bly on gold or other metal surfaces [9]. The use of redox-active
organometallic constituents assembled with all-carbon or hetero-
nitrogen containing Lewis-base connecting units [11].
We here describe the synthesis of MeC(O)S end-capped linear
homobimetallic palladium complexes in which the metal atoms
are bridged by organic nitrogen containing units of different size.
We chose palladium as metal centers because of their ability to
form stable metal–carbon and metal–nitrogen bonds and also sim-
ilar complexes are known, i.e. trans-[(C6H4-4-SC(O)Me)(Ph3P)2
(X)Pd] (X = halide, OTf) for comparison [12]. Cyclovoltammetric
studies of the newly prepared systems are reported as well.
2. Results and discussion
The synthesis protocol developed to prepare the homobimetal-
atomic p-spacers offer fascinating perspectives for the design and
lic rigid-rod structured palladium complexes [{trans-(MeC(O)S-4-
realization of rigid-rod structured species and hence, show several
advantages over organic ones [10].
Recently, we got interested in the design of transition metal
complexes featuring end-capped thiol or thio-acetyl groups and
their use as appropriate precursors for self-assembling on gold sur-
C6H4-C6H4)(Ph3P)2Pd}2(
(bpy); 8b,
-N\N = C5H4N-CH@N-N@CH-C5H4N; 8c,
C5H4N-CH@CH-C6H4-CH@CH-C5H4N; 8d,
-N\N = C5H4N-CH@N-
l l
-N\N)](OTf)2 (8a, -N\N = 4,40-bipyridine
l
l
-N\N =
l
C6H4-N@CH-C5H4N) is illustrated in Scheme 1. The therefore nec-
essary thiols 4-I-C6H4-C6H4-40-SC(O)Me (2) and trans-[(MeC(O)S-
4-C6H4-C6H4)(Ph3P)2Pd](OTf) (6) were synthesized via conven-
tional methods as outlined in Scheme 1.
* Corresponding author. Tel.: +49 371 531 21210; fax: +49 371 531 21219.
E-mail address: heinrich.lang@chemie.tu-chemnitz.de (H. Lang).
0022-328X/$ - see front matter Ó 2008 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2008.09.031

28
H. Lang et al. / Journal of Organometallic Chemistry 694 (2009) 27–35
O
1. t-BuLi
Pd(PPh3)4 (3)
2. 1/8 S8
I
I
Me
S
I
3. MeC(O)Cl
- 2 PPh3
1
2
O
O
PPh3
PPh3
[AgOTf] (5)
- AgI
Me
S
Pd
I
Me
S
Pd OTf
PPh3
PPh3
4
6
2+
O
O
2 OTf -
PPh3
Pd
PPh3
Pd
PPh3
(7)
0.5 N
N
1/2
Me
S
N
S
Me
N
PPh3
8a - 8d
Scheme 1. Synthesis of 2, 4, 6 and 8a–8d (Table 1).
4-Iodo-40-thioacetylbiphenyl (2) was accessible by the subse-
was reacted with silver-tetrafluoroborate and -triflate. However,
when [AgBF4] was used as a halide abstracting reagent, decompo-
sition of in situ-formed trans-[(MeC(O)S-4-C6H4-C6H4)(Ph3P)2-
Pd](BF4) occured even at low temperature. In contrast, treatment
of 4 with equimolar amounts of AgOTf (5) (TfO = triflate, OSO2CF3)
afforded trans-[(MeC(O)S-4-C6H4-C6H4)(Ph3P)2Pd](OTf) (6) in a tol-
uene-dichloromethane mixture of ratio 5:2 at 25 °C (Scheme 1).
While compound 6 could be handled in solution for a short period
of time without any decomposition, it appeared that attempts to
isolate 6 in crystalline form failed. Nevertheless, 6 could success-
fully be converted to the significant more stable homobimetallic
complexes 8\a–8d by addition of 0.5 equivalents of the Lewis-bases
N\N (7a, N N = 4,40-bpy; 7b, N\N@C5H4N-CH@N-N@CH-C5H4N;
7c, N\N = C5H4N-CH@CH-C6H4-CH@CH-C5H4N; 7d, N\N = C5H4N-
CH@N-C6H4-N@CH-C5H4N) (Scheme 1 and Table 1), whereby the
quent reaction of commercially available 4,40-diiodobiphenyl (1)
with tBuLi, 1/8 S8 and MeC(O)Cl in tetrahydrofuran at low temper-
ature (Scheme 1). After appropriate work-up, thioacetate 2 could
be isolated as a colorless solid in 80% yield. Treatment of 2 with
a stoichiometric amount of [(PPh3)4Pd] (3) in toluene at 25 °C pro-
duced by an oxidative addition of the C–I bond to palladium mono-
nuclear trans-[(I)(MeC(O)S-4-C6H4-C6H4)(Ph3P)2Pd] (4) as a stable
yellow solid in excellent yield (Scheme 1).
For the preparation of 8a–8d it was necessary to exchange the
iodo ligand in 4 for a more labile group. Therefore, molecule 4
Table 1
Synthesis of 8a–8d
labile OTf ligand in 6 was replaced by the better
r-donor/p-base
Compound
Yielda (%)
N\N.
N
N
Yellow-colored crystals of 8a–8d could be obtained by slow dif-
fusion of n-pentane into a dichloromethane solution containing 8
at room temperature. They are air-, moisture- and temperature-
sensitive. Due to their ionic nature, 8a–8d are only soluble in polar
organic solvents including tetrahydrofuran and dichloromethane,
whereas in acetonitrile, dimethylsulfide and dimethylformamide
8a
75
N
N
8b
8c
8d
84
83
81
N
N
N
N
N
N
N
N
N
N
Fig. 1. ORTEP diagram (50% probability level) of the molecular structure of 4 with
the atom-numbering scheme. One CH2Cl2 molecule as packing solvent, the
hydrogen atoms as well as the disordered atoms O10 and C500 have been omitted
for clarity.
a
Based on 4.

H. Lang et al. / Journal of Organometallic Chemistry 694 (2009) 27–35
29
Fig. 2. ORTEP diagram (50% probability level) of 8c with the geometry and atom-numbering scheme. The two triflate ions, the hydrogen atoms and the disordered atoms of
the phenylenethioacetate unit (C70–C140, O10, S10) have been omitted for clarity. Selected bond distances and angles are given in Table 3.
they rapidly decompose even at low temperature to give black
insoluble materials. On the other hand, solid 8a–8d are stable for
months under inert gas atmosphere at ꢀ30 °C.
4. However, for the acetyl group two very distinct resonances could
be observed at ca. 190 (CO) and 30 (CH3) ppm, respectively.
The 31P{1H} NMR spectrum of 4 in CD2Cl2 consists of a sharp
singlet at 22 ppm for the Pd(PPh3)2 unit. Compared with free
Ph3P [14] this signal is shifted to lower field, which is representa-
tive for the coordination of phosphanes to transition metal atoms.
In addition, the 31P{1H} NMR spectra of 8a–8d are coherent with
the formation of single, highly symmetrical species, since only
one sharp singlet appeared at ca. 20 ppm, 2 ppm up-field shifted
relative to 4.
Further structural informations for 4 and 8 were obtained by
single X-ray structure determination. Slow vapor diffusion of n-
pentane into a dichloromethane solution containing 4 or 8c at
25 °C led to the formation of yellow crystals of 4 and 8c, respec-
tively. The molecular structure of 4 is depicted in Fig. 1, while
Fig. 2 contains homobimetallic 8c. Selected bond distances (Å)
and angles (°) are listed in Table 2 (4) and Table 3 (8c). Crystallo-
graphic and structural refinement data are summarized in Table
5 (Section 3).
Compounds 2, 4 and 8a–8d were characterized by elemental
analysis, IR and NMR (1H, 13C{1H}, 31P{1H}) spectroscopy. From 4
and 8c the molecular solid state structures were determined (see
below).
The thioacetyl group in 2, 4 and 8 gives rise to a very character-
istic CO stretching vibration at ca. 1700 cmꢀ1 [13a]. This band is, as
expected, not significantly influenced, when one goes from 2 to 4
to 8. The triflate ion in 8a–8d shows a distinct mSO absorption at
ca. 1265 cmꢀ1 which is in agreement with the non-coordinating
character of this group [13]. This observation resembles to data
found for other transition metal complexes, i.e. {[(dppp)Pd][C6H4-
1,4-(C„N)2]2(OTf)2}4 (1280 cmꢀ1) [13].
The 1H NMR spectra of all complexes exhibit well-resolved res-
onance signals with the expected coupling pattern for each of the
organic groups present (C6H4-C6H4-4-SC(O)Me, C6H5, C5H4N,
C5H4N-CH@N, C5H4N-CH@CH, C6H4) (Section 3).
We were not able to obtain appropriate 13C{1H} NMR spectra for
8a–8d, since these systems are less soluble in common organic sol-
vents (vide supra). In addition, signal overlapping does not
unequivocally allow assigning the appropriate resonance signals
between 120 and 150 ppm in the 13C{1H} NMR spectra of 2 and
Complex 4 crystallizes in the monoclinic space group C2/c. The
coordination geometry around Pd1 is planar caused by the two
Table 4
Peak potentials and formal (redox) potentials of 2, 4 and 8a–8d (irr. designates a
current peak without a corresponding reverse peak)
a
Ep,ox
Ep,ox (S–
Ep,ox
Ep,red
E0
(
l
-N\N)
E0 (l
-N\N)
(Pd(II)/
Pd(IV))
C(O)Me) (C–I)
ligand 7a–7d
[30]
Table 2
Selected bond distances (Å), bond angels (°), and torsion angels (°) for 4a
2
4
–
1.26 V
(irr.)
1.48 V
(irr.)
1.09 V
(irr.)
1.66 V ꢀ1.09 V
–
–
–
Bond distances
Bond angles
Torsion angles
Pd1–C37 2.023(6)
C37–Pd1–P2 86.0(2)
C37–Pd1–P1 88.0(2)
P2–Pd1–P1
I1–Pd1–C37–C38
ꢀ162.5(9)
0.81 V
(irr.)
–
–
–
–
–
Pd1–P2
Pd1–P1
Pd1–I1
C46–S1
2.337(2)
2.350(2)
C41–C40–C43–C44 ꢀ140.6(7)
172.87(6) C41–C40–C43–C48 36.7(9)
8a 0.87 V
ꢀ1.75 V (irr.)
ꢀ2.51 V
2.6764(8) C37–Pd1–I1 171.7(2)
1.780(7)
C46–S1–C49–C50
S1–C46–C47–C48
C46–S1–C49–O1
C45–C46–S1–C49
174(2)
(irr.)
(DEp = 0.54 V)
P2–Pd1–I1
P1–Pd1–I1
C49–S1–C46 103.0(4)
91.86(5)
93.53(5)
174.8(7)
ꢀ13(2)
ꢀ3.08 V
Ep = 0.54 V)
ꢀ1.92 V
Ep = 0.23 V)
ꢀ2.30 V
Ep = 0.23 V)
C40–C43 1.484(9)
(D
S1–C49
1.709(9)
ꢀ100.7(7)
8b 0.82 V
1.06 V
(irr.)
–
–
ꢀ1.50 V
(irr.)
(D
Ep = 0.11 V)
(D
a
The estimated standard deviations of the last significant digit(s) are shown in
ꢀ1.67 V
Ep = 0.10 V)
ꢀ1.90 V
Ep = 0.13 V)
ꢀ1.50 V
Ep = 0.06 V)
ꢀ1.70 V
Ep = 0.06 V)
ꢀ1.10 V
Ep = 0.29 V)
ꢀ1.42 V
Ep = 0.15 V)
ꢀ1.71 V
Ep = 0.16 V)
parentheses.
(D
(D
(D
Table 3
8c 0.74 V
1.07 V
(irr.)
–
–
–
–
ꢀ2.21 V
Ep = 0.35 V)
ꢀ2.40 V
Ep = 0.33 V)
ꢀ2.00 V
Ep = 0.31 V)
ꢀ2.23 V
Ep = 0.31 V)
ꢀ2.48 V
Ep = 0.27 V)
Selected bond distances (Å), bond angels (°), and torsion angels (°) for 8ca
(irr.)
(D
(D
Bond distances
Bond angles
Torsion angles
(D
(D
8d 0.87 V
1.16 V
(irr.)
Pd1–C1 2.040(9) C1–Pd1–N1
Pd1–P2 2.350(3) C1–Pd1–P1
Pd1–P1 2.339(3) P2–Pd1–P1
Pd1–N1 2.153(7) N1–Pd1–P1
C10–S1 1.75(2)
S1–C13 1.56(2)
177.7(4)
89.0(3)
C53–C56–C57–C58 ꢀ174.6(13)
(irr.)
(D
(D
C3–C4–C7–C8
146.5(15)
5.4(18)
160(8)
177.78(9) C10–S1–C13–O1
90.7(2) C51–N1–Pd1–C1
(D
(D
C53–C56–C57 131.2(18)
C56–C57–C58 130(2)
(D
(D
a
a
Experiments were performed in THF, this explains in part the electrode
potential differences.
The estimated standard deviation(s) of the last significant digit(s) are shown in
parentheses.

30
H. Lang et al. / Journal of Organometallic Chemistry 694 (2009) 27–35
Table 5
trans-configurated iodo-palladium-carbon units in which likewise
the Pd–I bond is trans to a C-sp2 donor atom of high trans-influ-
ence [15–17].
Experimental data for the X-ray diffraction studies of 4 and 8c
4
8c
The structure of 8c in the solid state confirms the presence of a
Formula
Formula weight
Space group
Crystal system
Z
a (Å)
b (Å)
c (Å)
C50.5H42ClIOP2PdS
1027.59
C2/c
Monoclinic
8
21.758(4)
10.572(3)
39.496(10)
90
C61H49F3NO4P2PdS2
1149.47
P1
Triclinic
2
10.8177(10)
11.0865(11)
24.632(3)
87.008(2)
89.541(2)
79.414(2)
2899.5(5)
1.316
homobimetallic
rigid-rod
[{trans-(MeC(O)S-4-C6H4-C6H4)
-C5H4N-C@CH-C6H4-CH@CH-C5H4N)]2+ system and
ꢀ
(Ph3P)2Pd}2(
l
two non-coordinated triflate ions, while the asymmetric unit of
8c contains half of the cationic unit and one non-coordinated tri-
flate entity. The second part of the molecule is generated by an
inversion center in the center of the phenylene group of the con-
necting unit 7c. The organometallic dicationic part consists of
a
(°)
b (°)
99.224(6)
90
8967(4)
two planar MeC(O)S-4-C6H4-C6H4)(Ph3P)2Pd moieties and the
l-
c
(°)
bridging C5H4N-C@CH-C6H4-CH@CH-C5H4N entity (r.m.s. deviation
of Pd1–P1–P2–N1–C1 is 0.0214 Å) (Fig. 2).
Volume (Å3)
dcalc (g cmꢀ1
)
1.522
Temperature (K)
298(2)
4120
1.317
298(2)
1178
0.502
The interplanar angle between the two planes defined by the
phenylene groups of the MeC(O)S-4-C6H4-C6H4 moieties is 34.7°
which is characteristic for biaryls (for example, the interplanar an-
gle in biphenyl is close to 0° [18a]). In contrast, the biphenyl moi-
ety in 8c is planar (with significant thermal libration even at low
temperature) [18b]. Crystallographic interplanar angles for para-
nitro-, [18c] -dinitro- [18d], and -dimethylbiphenyl [18e] deriva-
tives exhibit values between 30° and 40°, whereas para-dihydroxy-
biphenyl is planar in the solid state [18f,18g]. The palladium–
nitrogen, palladium–phosphorus and palladium–carbon separa-
tions are in the typical range as observed for other palladium orga-
nometallic complexes [15,17].
F(000)
l
(Mo K
Crystal size (mm)
min, hmax (°)
h, k, l (min, max)
a
) (mmꢀ1
)
0.4 ꢁ 0.3 ꢁ 0.3
1.90, 25.69
ꢀ26, 0, 0; 26, 12, 48
19425, 8574
0.0593
0.0610, 0.1024
0.1354, 0.1516
1.015
0.4 ꢁ 0.2 ꢁ 0.1
1.66, 25.34
ꢀ13, ꢀ13, ꢀ13; 13, 0, 29
23711, 10323
0.0655
0.1036, 0.1655
0.2199, 0.2515
1.139
h
No. of total, unique reflections
R(int)
a
R1 [I > 2
r
(I)], all
b
wR2 [I > 2r (I)], all
S
Residual density (e/Åꢀ3
)
ꢀ0.868, 0.825
ꢀ1.275, 1.280
P
jjFo jꢀjFc jj
a
P
R1
¼
jFo
j
rffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi
P
2
wðF2o ꢀF2c
Þ
ðmaxðF2o ;0Þþ2F2c
Þ
Complex 8c shows intra- and intermolecular
pꢀp interactions
b
1
P
wR2
¼
with w ¼
P ; P ¼
2
2
wðF2o
Þ
r2 ðF2o Þþðg1PÞ þg2
3
resulting from the aryl ligands (N1, C51–C55 and C15–C20) form-
ing a 2-D layer in the solid state (Fig. 3). As it can been seen from
Fig. 3, five aryl rings interact with each other in a sandwich-type
arrangement [18h]. Further details are presented in Fig. 4. The
arrangement of these five aryl rings is thereby centrosymmetric,
with a inversion center in the middle of the central aryl ring
C58B–C60BA. The sandwich-type interaction is truncated after
the fifth aryl ring at the expense of the formation of T-shaped
trans-positioned phosphorus atoms P1 and P2, the
r-bonded io-
dide I1, and C37 of the C6H4-C6H4-4-SC(O)Me unit (Fig. 1)
(r.m.s. deviation of Pd1–P1–P2–I1–C37 is 0.0486 Å). The palla-
dium-bonded phenylene group of the biphenylene unit is thereby
nearly perpendicular oriented to the transition metal coordination
plane (93.1°), while the second C6H4 entity forms an interplanar
angle of 37.2°. The Pd1–P1 and Pd1–P2 separations with
2.350(2) and 2.337(2) Å are in the range expected for trans-posi-
tioned triphenyl phosphine ligands (2.319–2.360 Å) [15–17]. Both,
the Pd1–I1 (2.6764(8) Å) and the Pd1–C37 distance (2.023(6) Å)
(Table 2) agree well with those separations reported for other
p p interactions [18h], as depicted in Fig. 5 together with geomet-
ꢀ
rical details. The situation is further complicated with respect to
the disorder of the MeC(O)S-4-C6H4-C6H4 entity, therefore Fig. 5 in-
cludes only one MeC(O)S-4-C6H4-C6H4 moiety. Between adjacent
2-D layers no further
pꢀp interactions are present.
Fig. 3. Part of a 2-D layer of 8c illustrating the sandwich-type and T-shaped
p–p interactions between adjacent molecules. Hydrogen and oxygen atoms, and the triflate
anions have been obmitted for clarity.

H. Lang et al. / Journal of Organometallic Chemistry 694 (2009) 27–35
31
In order to gain a first insight into the electrochemical behavior
1.66 V
350
300
250
200
150
100
50
of the newly synthesized molecules, compounds 2, 4 and 8a–8d
have been subjected to cyclic voltammetry (CV) [19]. Of particular
importance is the behavior of molecule 2, proper understanding of
its electrochemistry provides the basis for the assignment of cur-
rent peaks in 4 and 8a–8d containing 2 as a building block.
A CV of 2 (Fig. 6) in dichloromethane shows two anodic oxida-
tion waves at Ep,ox = 1.26 V and Ep,ox = 1.66 V, caused by oxidation
of the thio-acetyl unit and the C–I unit, respectively, as reported
previously for molecule MeC(O)S-4-C6H4-C6H4-SC(O)Me at
Ep,ox = 1.16 V and 1.65 V [20].
1.26 V
j
Oxidation of the thioacetyl-unit has been observed previously
in the range Ep,ox = 1.3–1.45 V with a selection of similar molecules
[21–23], a discussion of the suggested reaction mechanism can be
found in Ref. [21]. Oxidation of the iodo substituent has been re-
ported for the structurally closely related 4,40-diiodobiphenyl
[20]. Two current peaks were observed at Ep,ox = 1.65 V and at
Ep,ox = 1.76 V. This spacing implies intramolecular communication
resulting in the measured shift of the second oxidation peak to
more positive values. The peak potential found in the present study
of the ‘‘mixed” molecule 2 falls well between the peak potentials
observed before. The absence of a significant shift of the oxidation
potential implies that the preceding oxidation of the thioacetyl
unit has no influence via intramolecular communication.
0
-1.09 V
-50
-2.5
-2.0
-1.5
-1.0
-0.5
0.0
0.5
1.0
1.5
2.0
2.5
EFeC / V
Fig. 6. Cyclic voltammogram of 2 in a solution of [n-Bu4N][PF6] (c = 0.1 mol dmꢀ1
)
in dichloromethane, 25 °C, argon, scan rate 100 mV sꢀ1, thin line: blank supporting
electrolyte solution only.
Scanning from the positive potential limit into the negative
direction yields a cathodic peak at Ep,red = ꢀ1.09 V persisting in
multicycle measurements. This peak does not appear, when the
Fig. 4. Geometrical details of the sandwich-type
p–p interactions of five aryl rings of 8c within a 2-D layer. Label ‘‘A” refers to atoms of a first, labels ‘‘B” and ‘‘BA” to atoms of
a second and label ‘‘C” to atoms of a third molecule of 8c, with d giving the center-to-center distances as well as the shortest and longest C–C distance of adjacent aryl rings.
Fig. 5. Geometrical details of the T-shaped p–p interaction [14h] between aryl rings of 8c within a 2-D layer. Label ‘‘A” refers to atoms of a second molecule of 8c, with d
giving the center-to-center distances.

32
H. Lang et al. / Journal of Organometallic Chemistry 694 (2009) 27–35
50
150
100
50
1.15 V
1.48 V
25
0
- 1.10 V
I
j
-25
-50
-75
0.81 V
0
-2.5
-2.0
-1.5
-1.0
-0.5
0.0
0.5
1.0
1.5
2.0
-2
-1
0
1
EFeC / V
EFeC / V
Fig. 7. Cyclic voltammogram of 4 in a solution of [n-Bu4 N][PF6] (c = 0.1 mol dmꢀ1
)
Fig. 8. Cyclic voltammogram of trans-[(Ph3P)2Cl2Pd] (bold line) in a solution of [n-
in dichloromethane, 25 °C, argon, scan rate 100 mV sꢀ1; thin line: blank supporting
Bu4N][PF6] (c = 0.1 mol dmꢀ1
) in dichloromethane, 25 °C, argon, scan rate
electrolyte solution only.
100 mV sꢀ1; thin line: blank supporting electrolyte solution only.
initial scan was performed from the starting potential E = 0.0 V into
the negative going direction. This implies that the reduction peak
at Ep,red = ꢀ1.09 V (Fig. 6) results from species formed by the oxida-
tion of the S–C(O)Me or the I entity. The assignment to the direct
reduction of the iodo ligand (as stated with Ep,red = ꢀ1.49 V else-
where [20]) can be excluded because the peak appears only after
a positive going potential excursion. This peak has been observed
instead in CV studies of 4-iodo-40-thioacetylbiphenyl at
Ep,red = ꢀ1.03 V confirming the lack of association with I reduction.
The suggested reduction of electrooxidation products of the thio-
acetyl unit has been discussed elsewhere in detail [21].
The CV of mononuclear trans-[(I)(C6H4-C6H4-4-SC(O)Me)(PPh3)2
Pd] (4) (Fig. 7) shows an oxidation current shoulder at Ep,ox = 0.81 V
which can be assigned to the oxidation of Pd(II).
Based on evidence reported elsewhere a transition from Pd(II)
to Pd(IV) has to be expected because Pd(III) is unstable [24,25].
Oxidation potentials pertaining to this reaction are scant. An oxida-
tion peak observed in a CV study of [(PPh3)2Hal2Pd] turned out to
be caused by the reoxidation of Pd(0) generated in a negative going
potential excursion [26], Campora et al. have reported a current
peak in CVs of Pd(II) complexes in the range from 1.06 V >
Ep,ox > 1.24 V1 which they assigned to the oxidation of Pd(II) to
Pd(IV) [27].
The cyclic voltammograms of 8a–8d display current shoulders
at Ep,ox = 0.87 and 1.09 for 8a, 0.82 and 1.06 V for 8b, 0.74 and
1.07 V for 8c and 0.87 and 1.16 V for 8d, respectively (for a com-
plete listing see Table 4). The former peaks can be assigned to
the oxidation of palladium(II), the latter to oxidation of the
SC(O)Me unit. The palladium oxidation shows a more positive va-
lue than with 4 indicating that the palladium atoms in 8a–8d are
more difficult to oxidize which can be explained by the
p-donor/
acceptor character of the connecting
l
-N\N units. A similar behav-
ior was previously reported for related compounds with similar
bridging units between ruthenium ions [28]. In addition, com-
plexes 8a–8d show, depending on the nature of the bridging N\N
moieties, one to three reduction peaks in the anodic region be-
tween ꢀ1.10 and ꢀ1.75 V. A similar electrochemical behavior
was found for [((PEt3)2)4(l
-4,40-bpy)2(anthracenyl)2Pt]4+ [29]. The
ligand reductions in 8a–8d are shifted to substantially less nega-
tive potentials in comparison with free 7a–7d (see Table 4) [30].
The differences are consistent with the expected electrostatic sta-
bilization of the negatively charged, reduced forms of the linking
units by the coordinated palladium cations [28,31,32].
3. Experimental
With trans-[(Ph3P)2Cl2Pd] a CV as displayed in Fig. 8 was ob-
tained, the oxidation of Pd(II) proceeds at Ep,ox = 1.15 V. The nega-
tive going peak at Ep,red = ꢀ1.1 V may indicate reduction of Pd(II) to
Pd(0).
General methods. All reactions were carried out in an atmo-
sphere of purified nitrogen (O2 traces: CuO catalyst, BASF AG, Lud-
wigshafen, Germany; H2O traces: molecular sieve, 4 Å, Roth
company) using standard Schlenk techniques. Solvents were puri-
fied by distillation (n-hexane and dichloromethane: calcium hy-
dride; toluene: sodium; tetrahydrofuran: sodium/benzophenone
ketyl). FT-IR spectra were recorded with a Perkin–Elmer FT-IR
1000 spectrometer (KBr). NMR spectra were recorded with a Bru-
ker Advance 250 spectrometer, operating in the Fourier transform
mode. 1H NMR spectra were recorded at 250.123 MHz (internal
standard, relative to CD2Cl2, d 5.32); 13C{1H} NMR spectra were re-
corded at 67.890 MHz (internal standard, relative to CD2Cl2, d
53.50). Chemical shifts are reported in d units (ppm) downfield
from tetramethylsilane with the solvent signal as reference signal.
31P{1H} NMR were recorded at 101.202 MHz in CDCl3 with
P(OMe)3 as external standard (d 139.0, relative to 85% H3PO4, d
0.00). Cyclic voltammograms (CVs) were recorded in a dried cell,
purged with purified argon at 25 °C. Platinum wires served as
working and as counter electrode. A calomel electrode served as
reference electrode. For ease of comparison, all potentials are con-
verted using the redox potential of the ferrocene-ferrocenium cou-
The lower oxidation potential observed here can be explained
by invoking the higher
r-electron-donating capability of the aryl
moiety (and perhaps even the iodo ligand) as compared to the
two chloro ligands resulting in a higher charge density at the pal-
ladium atom and hence, easier oxidation. The oxidation peak found
at Ep,ox = 1.48 V is assigned to the oxidation of the SC(O)Me group,
the upshifted value results from a transfer of charge density to the
palladium making oxidation more difficult. The absence of a corre-
sponding reduction peak implies a chemical follow-up reaction
resulting in species without redox activity in the scanned potential
region.
1
In the original report a saturated calomel electrode was used, as a reference the
redox process of [Fe(II)/(III)(g
5-C5H4(COMe))2] was used. The potential range given
here refers to this redox system, its formal potential may slightly differ from that of
the ferrocene/ferrocenium system used throughout this work.

H. Lang et al. / Journal of Organometallic Chemistry 694 (2009) 27–35
33
ple FcH/FcH+ (FcH = (
g
5-C5H5)2Fe) as reference (E0 = 0.00 V,
(d, 2H, JHH = 8.2 Hz, oH, C6H4-C6H4SC(O)CH3), 6.5 (dd, 2H,
4
D
EP = 0.10 V) [33,34]. Electrolyte solutions were prepared from
JHH = 8.2 Hz, JHP = 3.9 Hz, mH, C6H4-C6H4SC(O)CH3), 7.2–7.6 (m,
freshly distilled tetrahydrofuran and [n-Bu4N]PF6 (dried in oil-
pump vacuum at 120 °C). The organometallic complexes were
added at c = 1.0 mM. Cyclic voltammograms were recorded at a
scan rate of 100 mV sꢀ1 using a Radiometer system (VoltaLab
3.1) and a Radiometer Analytical PGZ 100 VoltaLab. Melting points
were determined using analytically pure samples, sealed off in
nitrogen-purged capillaries on a Gallenkamp MFB 595 010 melting
point apparatus. Microanalyses were performed by the Organic
Department at Chemnitz, Technical University and the Institute
of Organic Chemistry at the University of Heidelberg.
34H, C6H4-C6H4-4-SC(O)CH3 and PPh3). 31P{1H} NMR (CDCl3):
d = 21.7. 13C{1H} NMR (CDCl3): d = 30.1 (CH3), 125.2 (iC/C6H4),
126.3, 127.2 (C6H4), 127.7 (pt, C6H5, JCP = 4.9 Hz), 129.9 (C6H5),
131.9 (pt, iC/C6H5, JCP = 23.2 Hz), 134.0 (iC/C6H4), 134.5 (C6H4),
134.9 (pt, C6H5, JCP = 6.4 Hz), 136.0 (pt, C6H4, JCP = 5.0 Hz), 143.5
(iC/C6H4), 159.9 (iC/C6H4), 194.3 (CO).
4.3. Synthesis of 8a
AgOTf (5) (46.6 mg, 0.181 mmol) was added in a single portion
to 4 (178 mg, 0.181 mmol) dissolved in toluene–dichloromethane
(ratio 5:2) (40 mL) at 25 °C. After 30 min of stirring, the reaction
mixture was filtered through a pad of Celite. To this solution 7a
(14.0 mg, 0.090 mmol) was added and the resulting suspension
was stirred for 30 min. By addition of 50 mL of n-hexane a yellow
precipitate formed. The supernatant solution was removed by fil-
tration (canula) and the residue was dried in oil-pump vacuum.
Complex 8a was obtained as a yellow solid (147.1 mg, 0.065 mmol,
75% based on 4).
4. General remarks
Chemicals were purchased from commercial suppliers and were
used as received.
4.1. Synthesis of 2 (modified procedure Ref. [35])
4,40-Diiodobiphenyl (1) (5.00 g, 12.31 mmol) was dissolved in
tetrahydrofuran (300 mL) and t-BuLi (14.49 mL, 24.62 mmol,
1.7 M in n-pentane) was drop-wise added during 10 min at
ꢀ78 °C. After stirring this reaction solution at this temperature
for 10 min, sulfur (394 mg, 12.31 mmol) dissolved in tetrahydrofu-
ran (75 mL) was drop-wise added and the reaction mixture was al-
lowed to warm to 0 °C and stirred for 45 min at this temperature.
The solution was again cooled to ꢀ78 °C and acetylchloride
(966 mg, 13.31 mmol) was added in one portion. After warming
the reaction solution overnight to 25 °C, water (20 mL) was added
and the mixture was extracted with dichloromethane (3 ꢁ 50 mL).
The combined organic layers were dried over magnesium sulfate.
All volatiles were removed by rotary evaporation and the residue
was purified by chromatography (column size: 20 ꢁ 2.5 cm; Silica
gel; n-hexane–dichloromethane (ratio 10:3). Removal of the sol-
vents in oil-pump vacuum gave 2 as a colorless solid. Yield: 3.5 g
(9.88 mmol, 80% based on 1).
M.p.: 150 °C (dec.). Anal. Calc. for C112H90F6N2O8P4Pd2S4 ꢂ 0.5
CH2Cl2 (2213.38): C, 61.05; H, 4.14; N, 1.27. Found: C, 60.88; H,
4.17; N, 1.36%. IR (KBr): 3058 (m), 2924 (m), 1706 (s) (
(s), 1480 (s), 1434 (s), 1395 (sh), 1269 (vs) ( SO), 1153 (s), 1098
(s), 1065 (s), 1030 (s) ( CF), 1000 (s), 804 (s), 749 (s), 691 (s), 636
(s), 520 (vs) cmꢀ1 1H NMR (CD2Cl2): d = 2.4 (s, 6H, CH3), 5.29 (s,
mCO), 1608
m
m
.
0.5 CH2Cl2), 6.8 (d, 4H, JHH = 7.9 Hz, oH, C6H4-C6H4-4-SC(O)CH3),
6.9 (m, 8H, oH, C6H4-C6H4SC(O)CH3, C5H4N), 7.2–7.5 (m, 68H,
C6H4-C6H4-4-SC(O)CH3 and PPh3), 8.2 (m, 4H, mH, C5H4N). 31P{1H}
NMR (CD2Cl2): d = 19.7. 13C{1H} NMR data could not be obtained,
due to the low solubility of 8a in common NMR solvents.
4.4. Synthesis of 8b
Compound 4 (181.3 mg, 0.184 mmol) was dissolved in 40 mL of
a toluene–dichloromethane mixture of ratio 5:2 and one equiva-
lent of AgOTf (4) (47 mg, 0.184 mmol) was added at 25 °C in a sin-
gle portion. After 30 min of stirring at this temperature, the
reaction mixture was filtered through a pad of Celite. To the eluate,
7b (19 mg, 0.092 mmol) was added at 25 °C and the resulting sus-
pension was additionally stirred for 30 min. After appropriate
work-up (see synthesis of 8a), complex 8b could be isolated as a
yellow solid (168 mg, 0.076 mmol, 82% based on 4).
M.p.: 110–112 °C. IR (KBr): 2922 (m), 1904 (w), 1695 (vs) (mCO),
1475 (s), 1378 (m), 1351 (m), 1260 (m), 1121 (s), 1092 (s), 999 (s),
844 (m), 808 (vs), 762 (s), 693 (w), 679 (w), 618 (s), 555 (w), 526
(w), 496 (w) cmꢀ1 1H NMR (CD2Cl2): d = 2.4 (s, 3H, CH3), 7.3 (d,
.
2H, JHH = 8.2 Hz, oH, C6H4-4-SC(O)CH3), 6.5 (d, 2H, JHH = 8.2 Hz,
mH, C6H4SC(O)CH3), 7.1 (d, 2H, JHH = 8.2 Hz, mH, I-C6H4), 7.4 (d,
2H, JHH = 8.2 Hz, oH, I-C6H4). 13C{1H} NMR (CDCl3): d = 30.2 (CH3),
93.7 (C–I), 127.3 (iC/C6H4), 127.6 (C6H4), 128.9 (C6H4), 134.9
(C6H4), 137.9 (C6H4), 139.64 (iC/C6H4), 141.2 (iC/C6H4), 194.4
(CO). HRMS calcd. for C12H11IOS (M+) 354.9515, found 354.965.
M.p.: 155 °C (dec.). Anal. Calc. for C114H92F6N4O8P4Pd2S4
(2224.96): C, 61.54; H, 4.17; N, 2.52. Found: C, 61.26; H, 4.29; N,
2.58%. IR (KBr): 3054 (s), 2369 (w), 1703 (s) (
1479 (sh), 1476 (s), 1434 (s), 1353 (w), 1266 (vs (
(sh), 1152 (s), 1095 (s), 1062 (m), 1028 (vs) ( CF), 998 (s), 949
(m), 806 (s), 747 (s), 695 (vs), 636 (vs), 570 (sh), 516 (vs) cmꢀ1
m
CO), 1609 (m),
m
s(SO)), 1224
m
4.2. Synthesis of 4
.
1H NMR (CD2Cl2): d = 2.4 (s, 6H, CH3), 6.8 (d, 4H, JHH = 7.9 Hz, mH,
C6H4C6H4-4-SC(O)CH3), 7.0 (d, 4H, JHH = 8.1 Hz, mH, C5H4N-CH@N-
N@CH-C5H4N), 7.2 (m, 8H, oH, C6H4-C6H4-4-SC(O)CH3, C5H4N-
CH@N-N@CH-C5H4N), 7.2–7.4 (m, 68H, PPh3, C6H4-C6H4-4-
SC(O)CH3), 8.1 (d, 4H, JHH = 8.1 Hz, oH, C5H4N-CH@N-N@CH-
C5H4N), 8.2 (s, 2H, C5H4N-CH@N-N@CH-C5H4N). 31P{1H} NMR
(CD2Cl2): d = 19.7. 13C{1H} NMR (CD2Cl2): d = 30.4 (CH3), 127.3
(C5H4N), 127.6 (C6H4), 128.5(C6H5), 128.6 (C6H4), 129.4 (C6H5),
130.9, 134.3 (C6H4), 135.2, 137.2 (C6H5), 151.9 (C5H4N), 194.5 (CO).
Compound 2 (405 mg, 1.14 mmol) was dissolved in 50 mL of
toluene and one equivalent of [(PPh3)4Pd] (3) (1.32 g, 1.14 mmol)
was added in a single portion at 25 °C. During 2 h of stirring at this
temperature a yellow precipitate formed. All volatiles were re-
moved in oil-pump vacuum and the residue was dissolved in
dichloromethane (5 mL). n-Hexane (60 mL) was added, whereby
a yellow solid precipitated. The supernatant layer was decanted
and the residue was washed twice with n-hexane (20 mL) to gave
4 as a yellow solid. Yield: 0.95 g (0.96 mmol, 85% based on 2).
M.p.: 154 °C (dec.). Anal. Calc. for C50H41IOP2PdS (985.20): C,
60.96; H, 4.19; S, 3.25. Found: C, 61.09; H, 4.37; S, 3.87%. IR
4.5. Synthesis of 8c
(KBr): 3050 (m), 1697 (s) (mCO), 1575 (m), 1477 (s), 1434 (vs),
1401 (m), 1308 (w), 1261 (w), 1185 (w), 1158 (w), 1117 (s),
Complex 4 (157.9 mg, 0.160 mmol) was dissolved in a mixture
of toluene–dichloromethane (ratio 5:2) (40 mL) and then one
equivalent of AgOTf (4) (41.0 mg, 0.160 mmol) was added in a sin-
gle portion at 25 °C. After stirring this reaction solution for 30 min
1095 (sh), 1060 (m), 999 (s), 952 (m), 803 (s), 744 (s), 692 (vs),
618 (s), 519 (vs) cmꢀ1 1H NMR (CDCl3): d = 2.4 (s, 3H, CH3), 6.4
.

34
H. Lang et al. / Journal of Organometallic Chemistry 694 (2009) 27–35
it was filtered through a pad of Celite. To the thus obtained eluate,
7c (22.8 mg, 0.080 mmol) was added in a single portion at room
temperature and the resulting suspension was stirred for addi-
tional 30 min. On addition of 50 mL of n-hexane a yellow precipi-
tate formed. The supernatant solution was decanted and the
residue was dried in oil-pump vacuum. Complex 8c was obtained
as a yellow solid (153.0 mg, 0.067 mmol, 83% based on 4).
fully refined anisotropically in their local positions. The hydrogen
atom positions have been refined with a riding model. In 4 the half
occupied dichloromethane solvent molecule and the thioacetate
substituent are disordered and have been refined to split occupan-
cies of 0.35/0.65 (CH2Cl2) and 0.71/0.29 (O1, C50). In 8c the triflate
ion and the phenylenethioacetate unit are disordered and have
been refined to split occupancies of 0.77/0.23 (O3SCF3) and 0.50/
0.50 (C7–C14, O1, S1).
M.p.: 160 °C (dec.). Anal. Calc. for C122H98F6N2O8P4Pd2S4.CH2Cl2
(2384.01): C, 61.97; H, 4.23; N, 1.18. Found: C, 62.20; H, 4.28; N,
1.30%. IR (KBr): 3053 (m), 2922 (w), 1703 (s) (
(m), 1435 (s), 1401 (sh), 1266 (vs) ( SO), 1223 (sh), 1152 (s), 1095
(m), 1062 (w), 1029 (s) ( C–F), 998 (m), 965 (sh), 835 (s), 805 (s),
747 (s), 695 (s), 636 (s), 617 (sh), 559 (m), 518 (s) cmꢀ1 1H NMR
mCO), 1606 (s), 1476
Supplementary material
m
m
CCDC 679544 and 679545 contains the supplementary crystal-
lographic data for 4 and 8c. These data can be obtained free of
charge from The Cambridge Crystallographic Data Centre via
http://www.ccdc.cam.ac.uk/data_request/cif.
.
(CD2Cl2): d = 2.4 (s, 6H, CH3), 5.29 (s, 0.5 CH2Cl2), 6.8 (m, 8H, oH,
C6H4-C6H4-4-SC(O)CH3/mH, C5H4N-CH@CH-C6H4-CH@CH-C5H4N),
7.1 (s, 2H, C5H4N-CH@CH-C6H4-CH@CH-C5H4N), 7.2 (s, 2H, C5H4N-
CH@CH-C6H4-CH@CH-C5H4N), 7.3–7.4 (m, 68H, PPh3, C6H4-C6H4-
4-SC(O)CH3), 7.6 (s, 4H, C5H4N-CH@CH-C6H4-CH@CH-C5H4N),
7.9 (d, 4H, JHH = 6.8 Hz, oH, C5H4N-CH@CH-C6H4-CH@CH-C5H4N).
31P{1H} NMR (CD2Cl2): d = 19.9. 13C{1H} NMR (CD2Cl2): d = 30.0
(CH3), 122.2 (C5H4N), 126.8 (C6H4), 127.9, 128.3 (C6H5), 128.7
(C6H4), 128.8 (CH@CH), 130.8 (C6H4), 133.7 (C6H5), 133.9, 134.3
(C6H4), 135.1 (C6H5), 146.2 (CH@CH), 150.7 (C5H4N), 194.1 (CO).
Acknowledgements
We thank the Deutsche Forschungsgemeinschaft and the Fonds
der Chemischen Industrie for financial support. We are grateful to
Dr. S. Vatsadze, Moscow State University, Moscow (Russia) for a
generous gift of the pyridyl-based connecting species.
References
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reaction solution was filtered through a pad of Celite. To the eluate,
7d (22 mg, 0.076 mmol) was added at 25 °C and the resulting sus-
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M.p.: 144 °C (dec.). Anal. Calc. for C120H96F6N4O8P4Pd2S4
(2301.06): C, 62.64; H, 4.21; N, 2.43. Found: C, 62.40; H, 4.21; N,
2.43%. IR (KBr): 3054 (m), 2954 (w), 2274 (w), 1705 (s) (
1610 (m), 1575 (sh), 1476 (s), 1435 (s), 1351 (w), 1263 (vs) (
1223 (sh), 1152 (s), 1096 (s), 1060 (m), 1029 (vs) ( CF), 998 (s),
805 (s), 747 (s), 694 (vs), 637 (vs), 616 (s) cmꢀ1 1H NMR (CD2Cl2):
mCO),
m
SO),
m
.
(d) T. Ohgi, H.Y. Sheng, Z.C. Dong, H. Nejoh, Surf. Sci. 442 (1999) 277;
(e) T. Ohgi, D. Fujita, Z.C. Dong, H. Nejoh, Surf. Sci. 493 (2001) 453;
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