Biferrocene NCN pincer metal-d8 complexes: Synthesis, reaction chemistry and cyclovoltammetric studies

Article abstract of DOI:10.1016/j.jorganchem.2006.04.011

The synthesis of biferrocene-bridged NCN pincer palladium and platinum complexes (NCN = [1-C₆H₂(CH₂NMe₂)₂ -3,5]^-) is discussed. Sonogashira cross-coupling of [(η⁵-C₅H₄)Fe(η⁵-C ₅H₄C{triple bond, long}CH)]₂ (1) with I-1-NCN-4-X (2a, X = H; 2b, X = Br) produces [(η⁵-C₅H₄)Fe(η⁵-C ₅H₄C{triple bond, long}C-1-NCN-4-X)]₂ (3a, X = H; 3b, X = Br). Homobimetallic 3b further reacts with [Pd₂(dba)₃ · CHCl₃] (4) or [Pt(tol)₂(SEt₂)]₂ (5) (dba = dibenzylidene acetone, tol = 4-tolyl), respectively, to give tetrametallic [(η⁵-C₅H₄)Fe(η⁵-C ₅H₄C{triple bond, long}C-4-NCN-1-MBr)]₂ (6, M = Pd; 7, M = Pt) in which NCN-MBr fragments are connected by a biferrocene unit. Cyclovoltammetric studies show that the ferrocene moieties can independently be oxidized. The difference of the Fe(II)/Fe(III) redox couples amounts to ca. 300 mV and is not affected by the nature of the NCN pincer metal moities.

Full text of DOI:10.1016/j.jorganchem.2006.04.011

Journal of Organometallic Chemistry 691 (2006) 3319–3324
www.elsevier.com/locate/jorganchem
Biferrocene NCN pincer metal-d8 complexes: Synthesis,
reaction chemistry and cyclovoltammetric studies
a
b
b
a,
*
Stefan Ko¨cher , Gerard P.M. van Klink , Gerard van Koten , Heinrich Lang
a
Technische Universita¨t Chemnitz, Fakulta¨t fu¨r Naturwissenschaften, Institut fu¨r Chemie, Lehrstuhl Anorganische Chemie,
Straße der Nationen 62, 09111 Chemnitz, Germany
b
Debye Institute, Organic Synthesis and Catalysis, Utrecht University, Padualaan 8, 3584 CH Utrecht, The Netherlands
Received 12 January 2006; received in revised form 7 April 2006; accepted 18 April 2006
Available online 25 April 2006
Abstract
The synthesis of biferrocene-bridged NCN pincer palladium and platinum complexes (NCN = [1-C6H2(CH2NMe2)2-3,5]ꢀ) is dis-
cussed. Sonogashira cross-coupling of [(g5-C5H4)Fe(g5-C5H4C„CH)]2 (1) with I-1-NCN-4-X (2a, X = H; 2b, X = Br) produces [(g5-
C5H4)Fe(g5-C5H4C„C-1-NCN-4-X)]2 (3a, X = H; 3b, X = Br). Homobimetallic 3b further reacts with [Pd2(dba)3 Æ CHCl3] (4) or
[Pt(tol)2(SEt2)]2 (5) (dba = dibenzylidene acetone, tol = 4-tolyl), respectively, to give tetrametallic [(g5-C5H4)Fe(g5-C5H4C„C-4-
NCN-1-MBr)]2 (6, M = Pd; 7, M = Pt) in which NCN-MBr fragments are connected by a biferrocene unit. Cyclovoltammetric studies
show that the ferrocene moieties can independently be oxidized. The difference of the Fe(II)/Fe(III) redox couples amounts to ca. 300 mV
and is not affected by the nature of the NCN pincer metal moities.
ꢀ 2006 Elsevier B.V. All rights reserved.
Keywords: Biferrocene; NCN pincer; Iron; Palladium; Platinum; Tetrametallic; Cyclovoltammetry
1. Introduction
ray crystal structure analysis and, for example, 57Fe Mo¨ss-
bauer spectroscopy of a mixed valent salt showed non-
equivalence in the ferrocenyl building blocks [4d].
Recently, one-dimensional homo- and heterometallic
complexes in which the transition metal atoms are con-
nected by p-conjugated organic and/or inorganic units
have attracted great attention, due to their use as, for
example, molecular wires [1], sensors [2], or organometallic
polymers [3]. Complexes with reversibly switchable redox
active sites are particularly of interest, because they can
selectively adjust the electron density and electronic prop-
erties by oxidation or reduction. In this respect, biferrocene
is a most promising candidate to be used as a switchable
two-electron reservoir [4]. The redox-chemistry of biferro-
cene is characterized by two reversible one-electron couples
and electronic communication between the two (g5-
C5H5(g5-C5H4)Fe) moieties was found [4a]. Mono-oxida-
tion of the latter species selectively leads to a mixed-valence
Fe(II)–Fe(III) system with specific physical properties. X-
We here report on the synthesis and subsequent met-
allation of [(g5-C5H4)Fe(g5-C5H4C„C-4-NCN-1-X)]2
(NCN = [1-C6H2(CH2NMe2)2-2,6]ꢀ; X = H, Br) to give
novel tetrametallic complexes of structural type [(g5-
C5H4)Fe(g5-C5H4C„C-4-NCN-1-MBr)]2 (M = Pd, Pt).
Our strategy was to use biferrocene as both bridging units
and as redox center(s) between two NCN-MBr moieties,
because only less is known about functionalized polyferro-
cene derivatives which is attributed to the difficulty in
controlling the synthesis of such species.
2. Results and discussion
Following the Sonogashira cross-coupling protocol [5],
[(g5-C5H4)Fe(g5-C5H4C„CH)]2 (1) produces with 1-I-
C6H3(CH2NMe2)2-3,5 (2a) and 1-I-C6H2(CH2NMe2)2-3,5-
Br-4 (2b) in the presence of catalytic amounts of
*
Corresponding author. Tel.: +49 371 531 1673; fax: +49 371 531 1833.
E-mail address: heinrich.lang@chemie.tu-chemnitz.de (H. Lang).
0022-328X/$ - see front matter ꢀ 2006 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2006.04.011

3320
S. Ko€cher et al. / Journal of Organometallic Chemistry 691 (2006) 3319–3324
[(Ph3P)2PdCl2/CuI] in triethylamine as solvent the NCN-
functionalized biferrocenes [(g5-C5H4)Fe(g5-C5H4C„C-4-
NCN-1-X)]2 (NCN = [1-C6H2(CH2NMe2)2-3,5]ꢀ; 3a, X =
H; 3b, X = Br) (Eq. (1)). After appropriate work-up, 3a
and 3b can be isolated as red-brown solids in ca. 50% yield.
H
The solubility of 3a, 3b, 6 and 7 strongly decreases with
increasing molecular mass. Homobimetallic 3a and 3b are
nicely soluble in benzene or diethyl ether, whereas
tetrametallic 6 and 7 can only be dissolved in polar organic
solvents such as dichloromethane, chloroform, tetrahydro-
furan and acetonitrile, whereby 6 shows a somewhat better
solubility than 7. This can successfully be used in the
purification of 6, since this complex precipitates from
dichloromethane or chloroform by adding n-hexane. Due
to the lower solubility of 7 it was difficult to isolate
analytical pure samples (Section 4). However, ESI-TOF
mass spectrometric studies confirmed the proposed
structure of 7 with M+ at m/e = 1346.2. Further typical
fragments are M+ꢀC2H4PtBr (m/e = 1043.1) and
M+ꢀC2NCNPtBr+H (m/e = 851.1).
NMe2
R
Fe
[Pd / Cu]
+
2 I
Et3N, 4 h reflux
Fe
NMe2
H
1
2a, 2b
NMe2
R
Fe
NMe2
1
Compounds 3a, 3b and 6 were characterized by IR, H
Me2N
Fe
and 13C{1H} NMR spectroscopy and elemental analysis.
R
The spectroscopic data for 7 are partly presented as well.
R = H, Br
Me2N
1
As expected, the H NMR spectra of 3a, 3b and 6 in
3a, 3b
CDCl3 show for the cyclopentadienyl protons two reso-
nance signals with a AA0BB0 pattern and coupling con-
stants of 1.8 and 1.9 Hz, while for 7 only broad
resonance signals could be detected. The CH2 and NMe2
protons of the NCN ligands appear as singlets (Section
4). Upon introduction of a palladium or platinum atom
as given in complexes 6 and 7 a significant low-field shift
of these resonances is observed (3b: 2.34, 3.53; 6: 2.99,
3.99; 7: 3.11, 4.01 ppm).
ð1Þ
The standard lithiation–transmetallation procedure for the
complexation of palladium or platinum by NCN pincers [6]
could not be applied for 3a and 3b. Treatment of these species
t
with BuLi to generate the corresponding dilithium deriva-
tives followed by a quench with D2O did not result in the for-
mation of the respective deuterated NCN pincer molecules.
Another, and hence very effective option to prepare
NCN pincer complexes with late transition metals involves
the oxidative addition of carbon–bromide and –iodide
Most characteristic in the 13C{1H} NMR spectra of 3b
and 6 is the shift of the C(4) carbon atom to lower field,
when going from 3b (d(C–Br) = 126.0 ppm) to 6 (d(C–
PdBr) = 158.2 ppm). This indicates that C(4) becomes
deshielded, due to the presence of the palladium atom. Sim-
ilar downfield shifts are also found for the CH2 and NMe2
carbons (Section 4).
In the IR spectra of 3a, 3b, 6 and 7 the C„C stretching
vibrations is found at ca. 2210 cmꢀ1, showing that this
absorption band is not affected by the introduction of
palladium or platinum in 3. An analogues behaviour has
been observed for complexes with comparable structural
elements such as {Pt}(C„C)n{Pt} (n = 1,2; {Pt} = 4-
C6H2(CH2NMe2)2-2,6-PtCl-1) [6c].
bonds, respectively, to low-valent metal atoms
M
(M = Ni, Pd, Pt). [7] A suitable precursor for Pd(0) is
[Pd2(dba)3 Æ CHCl3] (dba = dibenzylidene acetone) (4) [8].
Reacting 3b with equimolar amounts of 4 for 18 h at
25 ꢁC in benzene yielded tetrametallic [(g5-C5H4)Fe(g5-
C5H4C„C-4-NCN-1-PdBr)]2 (6) in 66% yield (Eq. (2)).
The preparation of the orange colored, iso-structural
Fe2Pt2 complex [(g5-C5H4)Fe(g5-C5H4C„C-4-NCN-1-
PtBr)]2 (7) could be realized by refluxing 3b with stoichiom-
etric amounts of the platinum source [Pt(tol)2(SEt2)]2 (5)
(tol = 4-tolyl) in toluene.
NMe2
Br
Cyclovoltammetric studies were carried out with the
homobimetallic NCN-functionalized biferrocenes 3a and
3b and the tetrametallic biferrocene NCN pincer metal-d8
complexes 6 and 7 in tetrahydrofuran and dichloromethane
solutions at 25 ꢁC (Table 1). Exemplary, the obtained cyclic
voltammograms for 3b and 6 are depicted in Fig. 1.
The biferrocene-based transition metal compounds, 3a,
3b, 6 and 7 display the typical discrete one-electron, chem-
ically reversible oxidation waves E0,1 and E0,2 of the ferro-
cenyl units in the cyclovoltammograms which can be
assigned to the Fe(II)/Fe(III) redox couples (Table 1)
[1e,4c,4d,9].
Fe
NMe2
[Pd2dba3•CHCl3] (4) or
[Pt(tol-4)2(SEt2)]2 (5)
Me2N
Br
Fe
Me2N
3b
NMe2
M
Br
Fe
NMe2
Me2N
Fe
Br
M
Me2N
6, M = Pd
7, M = Pt
In 1 the two iron atoms can be reversibly oxidized at
E0,1 = +0.08 V and E0,2 = +0.40 V [9a]. Compared to 3a
and 3b these potentials are somewhat shifted to more
ð2Þ

S. Ko€cher et al. / Journal of Organometallic Chemistry 691 (2006) 3319–3324
3321
Table 1
3b. A similar shift was observed for the ferrocene-bridged
NCN pincer complexes Fe(g5-C5H4-NCNH)2 and Fe(g5-
C5H4-4-NCN-1-PdCl)2, respectively, in which the NCN
pincer unit is directly attached to the cyclopentadienyl
group [10,11].
The difference of the Fe(II)/Fe(III) redox couples (DE0,
Table 1) can be used to determine the stability of the
mixed-valence Fe(II)–Fe(III) species, relative to the iso-
valent Fe(II)–Fe(II)/Fe(III)–Fe(III) systems [9a,12]. The
values of the conproportionation constant KcFe2 for 3a,
3b, 6 and 7 are of similar order of magnitude and are within
the range as found for biferrocene (Table 1) [10]. This indi-
cates that the introduction of either a palladium(II) or plat-
inum(II) ion does not destabilize the mixed-valence Fe(II)–
Fe(III) species as it has been the case for other tetrametallic
biferrocene complexes [4,9a].
Electrochemical data of 3a, 3b, 6 and 7, and 1 for comparison
Compound
E0,1 [V]
(DEp [mV])
E0,2 [V]
(DEp [mV])
DE0 [mV]
KcFe2
Biferrocene [10]
ꢀ0.09
0.24
0.33
0.32
0.29
0.30
0.34
0.31
0.30
3.78 · 105
2.50 · 105
0.80 · 105
1.37 · 105
4.77 · 105
1.54 · 105
1.22 · 105
1 [9]
3aa
3ba
3bb
6b
0.08 (70)
0.40 (75)
0.24 (294)
0.32 (216)
0.32 (156)
0.28 (135)
0.26 (188)
ꢀ0.05 (270)
0.02 (215)
ꢀ0.01 (112)
ꢀ0.03 (115)
ꢀ0.04 (202)
7b
a
In tetrahydrofuran.
In dichloromethane.
b
35
30
25
20
15
10
5
Despite the generation of the oxidized species 3, 5 and 6
at the electrode surface on the electrochemical time scale,
we were not able to isolate mixed valence species. It was
found that, for example, chemical oxidation led to color
changes, but, however, always resulted in decomposition
of the appropriate oxidized systems.
The peak potential differences found for complexes 3, 5
and 6 are typical for oligo- and poly-ferrocenyl alkyne link-
ages, i.e. [(g5-C5H4)Fe(g5-C5H4C„CR)]2 (R = SiMe3, Fc)
and [(g5-C5H4)Fe(g5-C5H4(g2-C„CR)Co2(CO)6)]2 [4].
0
-5
-10
-0.7 -0.6 -0.5 -0.4 -0.3 -0.2 -0.1
0
0.1 0.2 0.3 0.4 0.5 0.6 0.7
E [V]
3. Conclusion
12
10
8
An efficient synthesis of tetrametallic biferrocene-based
complexes of structural type [(g5-C5H4)Fe(g5-C5H4-
C„C-NCN-MBr)]2 (M = Pd, Pt; NCN = [C6H2(CH2N-
Me2)2-2,6]ꢀ) by the oxidative addition of [(g5-C5H4)
Fe(g5-C5H4C„C-NCN-Br)]2 to the palladium(0) and
platinum(0) sources [Pd2(dba)3 Æ CHCl3] and [Pt(tol)2-
(SEt2)]2 is described. In these organometallic molecules dif-
ferent multiple electronegative transition metals are linked
by linear conjugated organic bridging units.
As it could be shown ethynyl biferrocenyl units can
function as excellent modular bridging entities in the con-
struction of complexes of higher nuclearity. Thus obtained
complexes possess reasonable stability in the solid state.
The ferrocenyl redox centers act independently of each
other, however, the biferrocene linking unit does not mod-
ulate the redox chemistry of the end-capped NCN-MBr
(M = Pd, Pt) building blocks. The peak potential differ-
ences DE for all new synthesized compounds result in only
a rough measure of electron communication.
6
4
2
0
-2
-4
-6
-8
-1.2
-1
-0.8 -0.6 -0.4 -0.2
0
0.2
0.4
0.6
0.8
1.0 1.2
E [V]
Fig. 1. Cyclic voltammograms of 3b (top) and 6 (bottom) in dichloro-
methane in the presence of [n-Bu4N][PF6] (c = 0.10 M) at 25 ꢁC under
argon at a scan rate of 100 mV sꢀ1. Potentials are referenced to the Cp2Fe/
Cp2Fe+ couple as internal standard (Cp2Fe = (g5-C5H5)2Fe, E0 = 0.00 V).
negative values, indicating that the introduction of NCN
pincer units at the biferrocene core only slightly influences
the electron density at the iron centres. Compound 3a is
more difficult to oxidize (+70 mV for the 1st and
+80 mV for the 2nd oxidation) than 3b, which is attributed
to the appropriate polarity of the C–H versus C–Br bond.
The group-10 transition metals palladium and platinum in
6 and 7 also affect the redox potentials of the two biferro-
cene iron atoms. The increased electron density leads to an
easier oxidation by 20 and 30 mV for the 1st and 40 and
60 mV for the 2nd wave for 6 and 7, respectively, versus
4. Experimental
4.1. General methods
All reactions were carried out under an atmosphere of
purified nitrogen using standard Schlenk techniques. Tetra-
hydrofuran, diethyl ether, benzene, toluene and n-hexane
were purified by distillation from sodium/benzophenone

3322
S. Ko€cher et al. / Journal of Organometallic Chemistry 691 (2006) 3319–3324
ketyl. Isopropylamine and triethylamine were dried by dis-
tillation from KOH. Infrared spectra were recorded with a
Perkin–Elmer FT-IR 1000 spectrometer. NMR spectra
were recorded with a Bruker Avance 250 spectrometer
(1H NMR at 250.12 MHz and 13C{1H} NMR at
62.86 MHz) in the Fourier transform mode. Chemical
shifts are reported in d units (parts per million) downfield
from tetramethylsilane with the solvent as the reference sig-
nal (CDCl3: 1H NMR, d = 7.26; 13C{1H} NMR, d = 77.0).
Cyclic voltammograms were recorded in a dried cell,
purged with purified argon at 25 ꢁC. Platinum wires served
as working and as counter electrode. A saturated calomel
electrode served as reference electrode. For ease of compar-
ison, all potentials are converted using the redox potential
of the ferrocene–ferrocenium couple Cp2Fe/Cp2Fe+
(Cp2Fe = (g5-C5H5)2Fe) as the reference (E0 = 0.00 V).
Electrolyte solutions were prepared from freshly distilled
tetrahydrofuran or dichloromethane and [n-Bu4N]PF6
(dried in oil-pump vacuum at 120 ꢁC, c = 0.1 M). The
respective organometallic complexes were added at
c = 1.0 mM. Cyclic voltammograms were recorded at a
scan rate of 100 mV sꢀ1 using a Radiometer Copenhagen
DEA 101 Digital Electrochemical Analyzer with an IMT
102 Electrochemical Interface. Melting points were deter-
mined using sealed nitrogen purged capillaries on a Gal-
lenkamp MFB 595 010M melting point apparatus.
Microanalyses were performed by the Department of
Organic Chemistry at Chemnitz, Technical University.
ESI-TOF mass spectra were recorded with a Mariner
ESI-TOF mass spectrometer (Applied Biosystems) operat-
ing in the positive-ion mode using dichloromethane as
solvent.
MgSO4, filtered through a pad of Celite, evaporated in oil-
pump vacuum and purified by column chromatography
(Silica gel, 7 · 5 cm) with diethyl ether and tetrahydrofuran
(ratio 1:1). The first yellow-orange band was discarded.
With methanol a 2nd fraction could be eluated. Evapora-
tion of the solvent in oil-pump vacuum afforded 3a as a
brown solid. Yield: 320 mg (0.40 mmol, 47% based on 2a).
M.p.: 64 ꢁC. IR (KBr): [cmꢀ1] 2212 (w) [mC„C]. 1H
NMR (CDCl3): [d] 2.25 (s, 24H, NMe2), 3.40 (s, 8H,
CH2N), 4.04 (pt, JHH = 1.9 Hz, 4H, C5H4), 4.22 (pt,
JHH = 1.9 Hz, 4H, C5H4), 4.26 (pt, JHH = 1.9 Hz, 4H,
C5H4), 4.43 (pt, JHH = 1.9 Hz, 4H, C5H4), 7.20 (t,
4
4JHH = 1.4 Hz, 2H, C6H3), 7.29 (d, JHH = 1.4 Hz, 4H,
C6H3). 13C{1H} NMR (CDCl3): [d] 45.3 (NCH3), 63.9
(NCH2), 65.9 (iC/C5H4), 68.1 (CH/C5H4), 69.8 (CH/
C5H4), 70.0 (CH/C5H4), 72.3 (CH/C5H4), 84.1 (iC/C5H4),
86.0 (FcC„C), 87.8 (FcC„C), 123.7 (iC/C6H3), 129.0
(CH/C6H3), 130.6 (CH/C6H3), 138.9 (iC/C6H3). Anal.
Calc. for C48H54Fe2N4 (798.66): C, 72.19; H, 6.82; N,
7.03. Found: C, 72.25; H, 6.67; N, 6.98%.
4.3.2. Synthesis of [(g5-C5H4)Fe(g5-C5H4C„C-4-NCN-1-
Br)]2 (3b)
Compound 3b was prepared according to the procedure
described for 3a, using 380 mg (0.91 mmol) of 1, 500 mg
(1.26 mmol) of 2b, 50 mg (0.07 mmol, 4.0 mol%) of
[(Ph3P)2PdCl2] and 14 mg (0.07 mmol, 4.0 mol%) of [CuI]
in 50 mL of triethylamine. The title compound was purified
by column chromatography over alumina using diethyl
ether as eluent for the 1st band and a mixture of diethyl
ether–tetrahydrofuran in the ratio of 3:2 for the 2nd frac-
tion. After evaporation of the solvents, 3b was obtained
as a red-brown solid. Yield: 305 mg (0.32 mmol, 51% based
on 2b).
4.2. General remarks
M.p.: 79 ꢁC. IR (KBr): [cmꢀ1] 2213 (w) [mC„C]. 1H
NMR (CDCl3): [d] 2.34 (s, 24H, NMe2), 3.53 (s, 8H,
CH2N), 4.06 (pt, JHH = 1.8 Hz, 4H, C5H4), 4.22 (pt,
JHH = 1.8 Hz, 4H, C5H4), 4.26 (pt, JHH = 1.8 Hz, 4H,
C5H4), 4.42 (pt, JHH = 1.8 Hz, 4H, C5H4), 7.40 (s, 4H,
C6H2). 13C{1H} NMR (CDCl3): [d] 45.6 (NCH3), 63.7
(NCH2), 65.7 (iC/C5H4), 67.9 (CH/C5H4), 69.7 (CH/
C5H4), 70.0 (CH/C5H4), 72.4 (CH/C5H4), 84.1 (iC/C5H4),
85.4 (C„C), 88.8 (C„C), 122.6 (iC/C6H2), 126.0 (iCBr/
C6H2), 131.7 (CH/C6H2), 138.7 (iC/C6H2). Anal. Calc.
for C48H52Br2Fe2N4 (956.45): C, 60.28; H, 5.48; N, 5.86.
Found: C, 59.93; H, 5.29; N, 5.76%.
[(g5-C5H4)Fe(g5-C5H4C„CH)]2 (1) [9], I-1-C6H3(CH2-
NMe2)2-3,5 (2a) [12], I-1-C6H2(CH2NMe2)2-3,5-Br-4 (2b)
[7], [Pd2(dba)3 Æ CHCl3] (4) [8], and [Pt(4-tol)2(SEt2)]2 (5)
[13,14] were prepared following published procedures. All
other chemicals were purchased from commercial suppliers
and were used without any further purification.
4.3. Synthesis
4.3.1. Synthesis of [(g5-C5H4)Fe(g5-C5H4C„C-1-
NCNH)]2 (3a)
Compound 1 (500 mg, 1.20 mmol) and 2 (540 mg,
1.70 mmol) were dissolved in 50 mL of diisopropylamine
and 70 mg (0.10 mmol, 4.0 mol%) of [(Ph3P)2PdCl2] and
20 mg (0.10 mmol, 4.0 mol%) of [CuI] were added. After
stirring the reaction mixture for 4 h at reflux, all volatiles
were removed (oil-pump vacuum). The reddish-brown res-
idue was then dissolved in 100 mL of diethyl ether and
extracted with a mixture of 100 mL of H2O and 5 mL of
4 M HCl. The aqueous phase was separated, treated with
30 mL of 1 M NaOH and extracted twice with 100 mL of
diethyl ether. The combined organic phases were dried over
4.3.3. Synthesis of [(g5-C5H4)Fe(g5-C5H4C„C-4-NCN-1-
PdBr)]2 (6)
60 mg (0.063 mmol) of 3b and 60 mg (0.058 mmol) of 4 in
15 mL of benzene were stirred for 18 h at 25 ꢁC. After-
wards, 20 mL of tetrahydrofuran were added and the reac-
tion mixture was stirred for 4 h at room temperature. All
volatiles were removed in oil-pump vacuum, the greenish-
black residue was dissolved in 20 mL of chloroform, filtered
through a pad of Celite, and concentrated in oil-pump vac-
uum to 3 mL. n-Hexane (30 mL) was added, whereby an

S. Ko€cher et al. / Journal of Organometallic Chemistry 691 (2006) 3319–3324
3323
(j) M.D. Ward, Chem. Soc. Rev. 24 (1995) 121;
(k) J.A. McCleverty, M.D. Ward, Acc. Chem. Res. 31 (1998)
842;
(l) H. Lang, Angew. Chem., Int. Ed. Engl. 33 (1994) 547;
(m) U.H.F. Bunz, Angew. Chem., Int. Ed. Engl. 35 (1996) 969;
(n) T.M. Swager, Acc. Chem. Res. 31 (1998) 201;
(o) M. Mayor, C. von Ha¨nisch, H.B. Weber, J. Reichert, D.
Beckmann, Angew. Chem., Int. Ed. Engl. 41 (2002) 1183;
(p) J.W. Ying, D.R. Sobraningh, G.L. Xu, A.E. Kaifer, T. Ren,
Chem. Commun. (2005) 357.
orange solid precipitated which was washed three times
with n-hexane (10 mL) and then with diethyl ether
(10 mL) to gave 6 as an orange solid. Yield: 45 mg
(0.038 mmol, 66% based on 4).
M.p.: 142 ꢁC (dec.). IR (KBr): [cmꢀ1] 2212 (w) [mC„C].
1H NMR (CDCl3): [d] 2.99 (s, 24H, N Me2), 3.99 (s, 8H,
CH2N), 4.05 (pt, JHH = 1.8 Hz, 4H, C5H4), 4.21 (pt,
JHH = 1.8 Hz, 4H, C5H4), 4.25 (pt, JHH = 1.8 Hz, 4H,
C5H4), 4.40 (pt, JHH = 1.8 Hz, 4H, C5H4), 6.88 (s, 4H,
C6H2). 13C{1H} NMR (CDCl3): [d] 53.7 (NCH3), 66.1
(iC/C5H4), 68.2 (CH/C5H4), 69.8 (CH/C5H4), 70.2 (CH/
C5H4), 72.4 (CH/C5H4), 74.3 (NCH2), 84.3 (iC/C5H4),
[2] (a) For example see P.D. Beer, P.A. Gale, G.Z. Chen, Coord. Chem.
Rev. 185–186 (1999) 3;
(b) O.B. Sutcliffe, M.R. Bryce, A.S. Batsanov, J. Organomet. Chem.
656 (2002) 211;
(c) P.D. Beer, E. Hayes, J. Coord. Chem. Rev. 240 (2003) 167;
(d) J. Razumiene, A. Vilkanauskyte, V. Gureviciene, V. Laurinavi-
cius, N.V. Roznyatovskaya, Y.V. Ageeva, M.D. Reshetova, A.D.
Ryabov, J. Organomet. Chem. 668 (2003) 83;
i
86.3 (C„), 87.2 (C„), 122.6 (CH/C6H2), 128.4 C/C6H2,
145.0 (iC/C6H2), 158.2 (iC/C6H2). Anal. Calc. for
C48H52Br2Fe2N4Pd2 Æ 1/2C6H6 (1169.29): C, 50.69; H,
4.59; N, 4.63. Found: C, 50.79; H, 4.10; N, 4.28%.
(e) M.J. Moloto, S.M. Nelana, R.M. Moutloali, I.A. Guzei, J.
Darkwa, J. Organomet. Chem. 689 (2003) 387.
[3] (a) W. Kaim, W. Bruns, S. Kohlmann, M. Krejcik, Inorg. Chim.
Acta 229 (1995) 143;
4.3.4. Synthesis of [(g5-C5H4)Fe(g5-C5H4C„C-4-NCN-1-
PtBr)]2 (7)
(b) M.H. Delville, Inorg. Chim. Acta 281 (1999) 1;
(c) I.R. Farrell, F. Hartl, S. Zalis, T. Mahabiersing, J. Chem. Soc.
Dalton Trans. (2000) 4323;
(d) R.D.A. Hudson, J. Organomet. Chem. 637–639 (2001) 47;
(e) A.S. Abd-El-Aziz, E.K. Todd, Coord. Chem. Rev. 246 (2003)
3;
100 mg (0.105 mmol) of 3b and 95 mg (0.102 mmol) of 5
dissolved in 15 mL of toluene were stirred at reflux for
5 min. The orange solution was cooled to 25 ꢁC, filtered
through a pad of Celite and concentrated in oil-pump vac-
uum to 5 mL. Upon addition of 20 mL of n-hexane an
orange precipitate formed, which was washed twice with
n-hexane (10 mL) and diethyl ether (10 mL) and dried in
oil-pump vacuum to afford 80 mg (0.059 mmol, 58% based
on 5) of 7.
(f) I. Fratoddi, C. Battocchio, A. Furlani, P. Mataloni, G. Polzonetti,
M.V. Russo, J. Organomet. Chem. 674 (2003) 10.
[4] (a) D.M. Hendrickson, S.M. Oh, T.Y. Dong, T. Kambara, M.J.
Cohn, M.F. Moore, Comm. Inorg. Chem. 4 (1985) 329;
(b) M.H. Delville, F. Robert, P. Gouzerh, J. Linares, K. Boukhedda-
den, F. Varret, D. Astruc, J. Organomet. Chem. 451 (1993)
C10;
M.p.: 159 ꢁC (dec.). IR (KBr): [cmꢀ1] 2211 (w) [mC„C].
3
1H NMR (CDCl3): [d] 3.11 (bs, JPtH = 34.8 Hz, 24H, N
(c) T.Y. Dong, M.J. Cohn, D.N. Hendrickson, C.G. Pierpont, J.
Am. Chem. Soc. 107 (1985) 4478;
(d) T.Y. Dong, D.N. Hendrickson, C.G. Pierpont, M.F. Moore, J.
Am. Chem. Soc. 108 (1986) 963;
(e) L.A. Hore, C.J. McAdam, J.L. Kerr, N.W. Duffy, B.H. Robinson,
J. Simpson, Organometallics 19 (2000) 5039;
(f) Y. Mori, T. Kasai, T. Takesada, H. Komatsu, H. Yamazaki, M.
Haga, Chem. Lett. (2001) 996;
Me2), 4.01 (bs, 8H, CH2N), 4.04 (bs, 4H, C5H4), 4.25 (bs,
8H, C5H4), 4.41 (pt, JHH = 1.8 Hz, 4H, C5H4), 6.91 (s,
4H, C6H2). ESI-TOF MS [m/z (rel. int.)] 1346.2 (15)
[M+], 1043.1 (10) [M+ꢀC2H4BrPt], 858.1 (100)
[M+ꢀC2NCNPtBr+H]. Anal. Calc. for C48H52Br2Fe2-
N4Pt2 (1346.61): C, 42.81; H, 3.81; N, 4.16. Found: C,
42.60; H, 3.91; N, 4.38%.
(g) T.Y. Dong, B.R. Huang, S.M. Peng, G.H. Lee, M.Y. Chiang, J.
Organomet. Chem. 659 (2002) 125;
(h) T.Y. Dong, C.K. Chang, S.H. Lee, L.L. Lai, M.Y.N. Chiang, K.
Lin, J. Organometallics 16 (1997) 5816;
Acknowledgement
(i) T.Y. Dong, L.S. Chang, I.M. Tseng, S.J. Huang, Langmuir 20
(2004) 4471;
(j) T.Y. Dong, H.W. Shih, L.S. Chang, Langmuir 20 (2004)
9340.
We are grateful to the Deutsche Forschungsgemeins-
chaft for financial support.
[5] K. Sonogashira, Y. Tohda, N. Hagihara, Tetrahedron Lett. 50 (1975)
4467.
References
[6] (a) D.M. Grove, G. van Koten, J.N. Louwen, J.G. Noltes, A.L.
Spek, H.J.C. Ubbels, J. Am. Chem. Soc. 104 (1982) 6609;
(b) M.C. Lagunas, R.A. Gossage, A.L. Spek, G. van Koten,
Organometalics 17 (1998) 731;
[1] (a) For example C.T. Chen, K.S. Suslick, Coord. Chem. Rev. 128
(1993) 293;
(b) F. Paul, C. Lapinte, Coord. Chem. Rev. 178–180 (1998) 431;
(c) C. Hortholary, C. Coudret, J. Org. Chem. 68 (2003) 2167;
(d) S. Rigaut, J. Perruchon, L. Le Pichon, D. Touchard, P.H.
Dixneuf, J. Organomet. Chem. 67 (2003) 37;
(c) S. Back, M. Lutz, A.L. Spek, H. Lang, G. van Koten, J.
Organomet. Chem. 620 (2001) 227.
´
[7] G. Rodrıguez, M. Albrecht, J. Schoenmaker, A. Ford, M.
(e) T.Y. Dong, M.C. Lin, M.Y.N. Chiang, J.Y. Wu, Organometallics
23 (2004) 3921;
Lutz, A.L. Spek, G. van Koten, J. Am. Chem. Soc. 124 (2002)
5127.
(f) A. Avrim, M. Ratner, in: Molecular Electronics: Science and
Technology, The New Academy of Science and Technology, New
York, 1998;
(g) J.M. Tour, Acc. Chem. Res. 33 (2000) 791;
(h) D. Astruc, Acc. Chem. Res. 30 (1997) 383;
(i) J.P. Launay, Chem. Soc. Rev. 30 (2001) 386;
[8] S. Komiya, Synthesis of Organometallic Compounds, Wiley, Win-
chester, UK, 1997.
[9] (a) M.C.B. Colbert, D. Hodgson, J. Lewis, P.R. Raithby, N. Long,
J. Polyhedron 14 (1995) 2759;
(b) N.J. Long, A.J. Martin, R. Vilar, A.J.P. White, D.J. Williams,
M. Younus, Organometallics 18 (1999) 4261.

3324
S. Ko€cher et al. / Journal of Organometallic Chemistry 691 (2006) 3319–3324
[10] N. Comire, U.T. Muller-Westerhoff, W.E. Geiger, J. Organomet.
¨
[13] H.P. Dijkstra, M.D. Meijer, J. Patel, R. Kreiter, G.P.M. van Klink,
M. Lutz, A.L. Spek, A.J. Canty, G. van Koten, Organometallics 20
(2001) 3157.
[14] (a) B.R. Steele, K. Vrieze, Transition Met. Chem. 2 (1977) 140;
(b) A.J. Canty, J. Patel, B.W. Skelton, A.J. White, J. Organomet.
Chem. 599 (2000) 195.
Chem. 637–639 (2001) 823.
[11] S. Ko¨cher, G.P.M. van Klink, G. van Koten, H. Lang, J. Organomet.
Chem. 684 (2003) 230.
[12] (a) D.E. Richardson, H. Taube, Coord. Chem. Rev. 60 (1984) 107;
(b) C. Creutz, Prog. Inorg. Chem. 30 (1983) 73.