Synthesis, redox activity of rigid ferrocenyl dendrimers, and isolation of robust ferricinium and class-II mixed-valence dendrimers

Article abstract of DOI:10.1002/chem.201300560

The coupling reactions of ethynylferrocene with trihalogenoarenes do not lead to ethynylferrocenyl arenes that are soluble enough to form the basis of a suitable construction of stiff ferrocenylethynyl arene-cored dendrimers, which explains the previous lack of reports on stiff ferrocenyl dendrimers. However, rigid ferrocenyl-terminated dendrimers have been synthesized from 1,3,5-tribromo- and triiodobenzene through Sonogashira and Negishi reactions with 1,2,3,4,5-pentamethyl-1-ethylnylferrocene (1 a), according to 1→2 connectivity. With compound 1 a, the construction of a soluble dendrimer (10 a) that contained 12 ethynylpentamethylferrocenyl termini was achieved. Stiff dendrimer 10 a shows a single, reversible cyclic voltammetry (CV) wave (with adsorption), which disfavors the hopping heterogeneous electron-transfer mechanism that is postulated for redox-terminated dendrimers that contain flexible tethers. The selectivity of these Sonogashira reactions allows the synthesis of an arene-cored dendron (2 c) that contains both ethynylferrocenyl and 1,2,3,4,5-pentamethyl-ferrocenylethynyl redox groups, thus leading to the construction of a dendrimer (7 c) that contains both types of differently substituted ferrocenyl groups with two well-separated reversible CV waves. Upon selective oxidation, this mixed dendrimer (7 c) leads to a class-II mixed-valence dendrimer, 7 c[PF₆]₃, as shown by Moessbauer spectroscopy, whereas oxidation of the related fully pentamethylferrocenylated dendrimer (7 a) leads to the all-ferricinium dendrimer, 7 a[PF₆]₆. Win or robust: Selective Sonogashira reactions with 1,3,5-tribromobenzene allowed the introduction of both ferrocenylethynyl and pentamethylferrocenylethynyl redox groups around stiff dendrimers, which led to the synthesis of both fully oxidized (ferricinium) dendrimers with 6 or 12 redox groups and a class-II mixed-valence dendrimer (see figure). Copyright

Full text of DOI:10.1002/chem.201300560

FULL PAPER
DOI: 10.1002/chem.201300560
Synthesis, Redox Activity of Rigid Ferrocenyl Dendrimers, and Isolation of
Robust Ferricinium and Class-II Mixed-Valence Dendrimers
Abdou K. Diallo, Jaime Ruiz, and Didier Astruc*[a]
Abstract: The coupling reactions of
ethynylferrocene with trihalogeno-
ACHTUNGTRENNUNGarenes do not lead to ethynylferrocenyl
soluble dendrimer (10a) that contained
12 ethynylpentamethylferrocenyl termi-
ni was achieved. Stiff dendrimer 10a
shows a single, reversible cyclic voltam-
metry (CV) wave (with adsorption),
which disfavors the hopping heteroge-
neous electron-transfer mechanism that
is postulated for redox-terminated den-
drimers that contain flexible tethers.
The selectivity of these Sonogashira re-
actions allows the synthesis of an
arene-cored dendron (2c) that contains
both ethynylferrocenyl and 1,2,3,4,5-
pentamethyl-ferrocenylethynyl redox
groups, thus leading to the construction
of a dendrimer (7c) that contains both
types of differently substituted ferro-
cenyl groups with two well-separated
reversible CV waves. Upon selective
oxidation, this mixed dendrimer (7c)
leads to a class-II mixed-valence den-
arenes that are soluble enough to form
the basis of a suitable construction of
stiff ferrocenylethynyl arene-cored den-
drimers, which explains the previous
lack of reports on stiff ferrocenyl den-
drimers. However, rigid ferrocenyl-ter-
minated dendrimers have been synthe-
sized from 1,3,5-tribromo- and triiodo-
benzene through Sonogashira and
Negishi reactions with 1,2,3,4,5-pen-
tamethyl-1’-ethylnylferrocene (1a), ac-
cording to 1!2 connectivity. With
compound 1a, the construction of a
drimer, 7cACHTNUTRGNEUNG[PF6]3, as shown by Mçssba-
uer spectroscopy, whereas oxidation of
the related fully pentamethylferroceny-
lated dendrimer (7a) leads to the all-
Keywords: cross-coupling
·
den-
drimers · electrochemistry · ferro-
cene · mixed-valence compounds
ferricinium dendrimer, 7aACTHNUTGRNEG[UN PF6]6.
Introduction
linear optical properties of a series of stiff dendrimers that
contain ruthenium complexes.[13] Giant polyarylene den-
drimers also illustrative examples with these properties, as
well as for biological applications in molecular recogni-
tion.[8,12] Recently, Yamamoto’s group introduced ferrocene
derivatives into rigid polyazidomethine dendrimers by em-
ploying non-covalent charge-transfer interactions.[14] Voll-
hardt and co-workers reported the “impossible” hot mole-
cule hexaferrocenylbenzene[15a] and, earlier, star-shaped
Electron-transfer reactions in multi-redox nanosystems, such
as polymers,[1] dendrimers[2] and other nanoparticles,[3] are of
interest for their relevance to biological redox processes,[4]
molecular conductors and semiconductors,[5] mixed-valence
stabilization,[6] catalysis,[7] and redox recognition.[8] Among
the redox systems that are involved in dendritic frameworks,
ferrocenes occupy a privileged place because of the stability
of both their FeII and FeIII forms, at least on the electro-
chemical timescale.[9] Although rigid dendrimers are
known,[10–13] there are no reports of rigid ferrocene-contain-
ing dendrimers, presumably because of the synthesis prob-
lems related to their insolubility. Rigid dendrimers have
been pioneered on the organic side by the work of Moore’s
group with polyarylene dendrimers[1] and on the inorganic
side by the reports of Balzani’s group on redox- and photo-
active ruthenium and osmium poly(oligopyridine) dendrim-
ers that are of specific interest as antenna models and for
their optoelectronic properties.[2] Since the late 1990s, Hum-
phrey and co-workers have synthesized and studied the non-
(diynyl)benzene.[15b,c] Re-
hexaACTHNUTRGNEN(UG ethynyl)benzene and hexaCAHTUNGTRENNUGN
cently, we also reported hexa(ferrocenylethyl)benzenes and
their related electrostatic effects.[16] Herein, we report a con-
vergent synthesis of rigid hexa- and dodecaferrocenyl arene-
centered poly(ethynylphenylene) dendrimers with C3 sym-
metry and 1!2 connectivity,[17] their electron-transfer prop-
erties, and the stabilization and isolation of ferricinium and
class-II mixed-valence ferrocenyl dendrimers.
Results and Discussion
The convergent synthesis of the metallodendrimers that
were used herein involved the Pd0-catalyzed Sonogashira re-
actions[18] of ethynylferrocenes with 1,3,5-tribromobenzene.
Whereas the Negishi reaction[19] of ferrocenylethynylzinc
chloride with hexabromobenzene was reported to yield
[a] Dr. A. K. Diallo, Dr. J. Ruiz, Prof. Dr. D. Astruc
Institut des Sciences Molꢀculaires, UMR CNRS No. 5255
Univ. Bordeaux , 33405 Talence Cedex (France)
E-mail: d.astruc@ism.u-bordeaux1.fr
hexaACHTNUGRTNEUNG
(ferrocenylethynyl)benzene,[16] the Sonogashira reaction
was much slower and selective because the favorable effect
of the electron-withdrawing halogen atoms decreased with
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/chem.201300560.
Chem. Eur. J. 2013, 19, 8913 – 8921
ꢁ 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
8913

increasing substitution. Indeed, with 1,3,5-tribromobenzene,
the Sonogashira reactions of the ethynylferrocenes rapidly
yielded the monoethynylation products and, more slowly,
the corresponding products of a second ethynylation step.
On the other hand, the third ethynylation step, which re-
quired a reaction time of one week, could be easily avoid-
ed. We have taken advantage of this selectivity to carry
Cp2Fe+/Cp2Fe). Contrary to the case of the star-shaped com-
plex hexa(pentamethylferrocenylethynyl)benzene,[16] no
electrostatic effect is observed by CV wave-splitting, even
upon using the weak-ion-pairing salt [nBu4]
ACHTUNGTERNNUNG
4
3,5-C6H3A
CTHUNGTRENNUNG
the relatively remote location of the redox groups from one
another in compound 7a. Because the electrostatic effect is
close to zero, the binomial-law statistics indicate the pres-
ence of 31% mixed-valence FeII FeIII dendrimer upon oxi-
out the convergent construction of poly(ferrocenylACTHNUGRTNEUNGethynyl)
dendrons, as shown in Scheme 1. Although 1,3-di(ferro-
cenylethynyl)-5-bromobenzene can be synthesized,[20] the
convergent syntheses cannot progress any further, because
of the insolubility of the hoped-for products. However, with
1,2,3,4,5-pentamethyl-1’-ethynyl ferrocene,[21] this draw-
back could be avoided and hexametallic dendrimer 7a was
successfully synthesized from the reaction of new metalla-
3
3
dizing half of compound 7a in a homogeneous solution. The
permethylated C5Me5 (Cp*) ring on the pentamethylferro-
cenyl termini in dendrimer 7a allows a much better stabili-
zation of the ferricinium species than the parent ferrocenyl
dendrimers. Indeed, the synthesis of the fully oxidized, blue
pentamethylferricinium dendrimer was carried out upon oxi-
A
dation of compound 7a with [Cp2Fe]
ACHTUNGTRENNUNG
Scheme 1.
CH2Cl2, thus leading to the isolation of complex 7aACHTUNGTRENNUNG
The cyclic voltammogram (CV) of compound 7a in
CH2Cl2 on a Pt anode shows a fully chemically and electro-
chemically reversible six-electron wave at ꢀ0.5 V (versus
stable deep-blue microcrystals. The d5, 17-electron electronic
structure of this complex is shown by the rhombic distortion
of the EPR signal. This synthesis represents a rare example
of a ferricinium dendrimer.[23]
Remarkably, the monopenta-
methylferrocenylethynylation
of 1,3,5-tribromobenzene with
compound 1a can be selective,
thereby giving the correspond-
ing monopentamethylferrocenyl
arene derivative (8), which
readily and selectively under-
goes
ferrocenylethynylation
with ethynylferrocene. In this
way, mixed, unsymmetrical di-
AHCTUNGTRENGNsUN ubstituted arene derivative 2c
was readily synthesized and fur-
ther used in the dendrimer syn-
thesis without being marred by
solubility problems. Thus, either
bis-1,3-(pentamethylferrocen-
yl)-5-ethynylbenzene
3a
(Scheme 1) or its unsymmetri-
cal mixed homologue (3c,
Scheme 2) reacted with 1,3,5-
triiodobenzene to give symmet-
rical
AHCTUNGTRENGNeUN thynyl
pentamethylferrocenyl-
dendrimer 7a
(Scheme 1) or mixed dendrimer
7c (Scheme 2), respectively, the
first of which containing two
distinct types of ferrocenyl
groups.
The reaction of compound 7a
with [FeCp2]
ACHTUNGTRENNUNG
CH2Cl2
hexapentaACTHUNGTRENNUNG
dendrimer 7aCAHTUNGTRENNNUG
precipitated by the addition of
diethyl ether, thus affording the
Scheme 1. Sonogashira synthesis of the hexa(pentamethylferrocenyl) G1 dendrimer.
8914
www.chemeurj.org
ꢁ 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2013, 19, 8913 – 8921

Robust Ferricinium and Class-II Mixed-Valence Dendrimers
FULL PAPER
ingly, the more easily oxidizable
pentamethylferrocenyl groups
are also those that give the
more robust ferricinium groups.
Thus, mixed-valence ferricini-
um/ferrocene
dendrimer
7c[PF6]3 is robust, unlike genu-
AHCTUNGTRENNUNG
ine ferricinium derivatives that
lack ring permethylation, which
are sensitive to air and polar
solvents. Various characteriza-
tion methods were used to con-
firm the structure of complex
7cACTHNURGTNEG[UN PF6]3, including elemental
analysis and IR, UV/Vis, EPR,
and Mçssbauer spectroscopy.
Its d5, 17-electron electronic
structure is shown by the rhom-
bic distortion in the EPR
signal. The class-II mixed-FeII/
FeIII valence is shown in the
zero-field Mçssbauer spectrum
of compound 7c by the pres-
ence of both the classical ferro-
cenyl-type doublet and the
quadrupole doublet, with a very
small value, which collapses
into a broad singlet that is char-
acteristic of ferricinium deriva-
tives. (Figure 3).[24]
CV wave-splitting in ferro-
cenyl dendrimers has previously
been observed by Casado’s
group with SiFc2 branch termini
(Fc=ferrocenyl); in that case,
such wave-splitting was a signa-
ture of mixed-valence stabiliza-
tion, but the oxidized or mixed-
Scheme 2. Sonogashira synthesis of the mixed ferrocenyl–pentamethylferrocenyl G1 dendrimer.
complex as deep-blue microcrystals (Scheme 3). This hexa-
pentamethylferricinium dendrimer was characterized by,
among other things, elemental analysis and by the single
broad band at I.S.=0.6 mmsꢀ1 (vs. Fe) and the nil quadru-
pole splitting, known for ferricinium derivatives, in the zero-
field Mçssbauer spectrum at 78 K (Figure 1).
valence dendrimers were not isolated.[26]
Various characterization methods were used to confirm
the structure of complex 7cACHTNUGTRNEUGN[PF6]3, including elemental anal-
ysis and IR, UV/Vis (see the Supporting Information), and
Mçssbauer spectroscopy. The class-II mixed-FeII/FeIII va-
lence is shown in the zero-field Mçssbauer spectrum of com-
The CV of mixed dendrimer 7c in CH2Cl2 on a Pt anode
shows two fully chemically and electrochemically three-elec-
tron reversible waves (Figure 2): One at E1/2 =ꢀ0.50 V (vs.
plex 7cACHTNUGRETNNU[G PF6]3 at 78 K by the presence of both the classical
ferrocenyl-type doublet and the quadrupole doublet, with a
quadrupole splitting, which collapse into a broad singlet that
is characteristic of ferricinium derivatives (Figure 3).[24]
Further convergent dendronic construction involved the
same Sonogashira reaction with 1,3,5-trimomobenzene,
which was stopped after one day to essentially afford the
substitution of only two bromine atoms of 1,3,5-tribromo-
benzene and the formation of dendron 11a, which contained
four iron-sandwich units. The third bromine atom was sub-
stituted by an ethynyl group upon Sonogashira reaction with
trimethylsilylacetylene or Negishi reaction with trimethyl-
+
CpFe2 /Cp2Fe), which corresponds to the oxidation of the
three pentamethylferrocenyl groups, and the other at E1/2
=
+
ꢀ0.25 V (vs. CpFe2 /Cp2Fe), which corresponds to the oxi-
dation of three ferrocenyl groups. This CV wave-splitting
shows the stabilization of the mixed-valence trication, with a
comproportionation constant (Kc) of the order of 104.
The partial oxidation of compound 7c was performed by
using [FeCp2]
dendrimer 7c[PF6]3, which was precipitated as brown micro-
crystals by the addition of diethyl ether (Scheme 4). Gratify-
ACHTUNGTRENNUNG[PF6] (3 equiv) in CH2Cl2 and yielded metallo-
ACHTUNGTRENNUNG
AHCTUNGTREGsNNUN ilylethynylzinc chloride, followed by deprotection, thus
Chem. Eur. J. 2013, 19, 8913 – 8921
ꢁ 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
8915

D. Astruc et al.
Scheme 3. Oxidation of pentamethylferrocenyl (7a) and mixed pentamethylferrocenyl–ferrocenyl dendrimers (7c) and the isolation of thermodynamical-
ly stable, fully oxidized hexacationic (7aACTHNUTRGENN[GU PF6]6) and mixed-valence tricationic dendrimers (7cAHCTUNGTRENN[UNG PF6]3).
Figure 2. CV of dendrimer 7c (c=1 mm in CH2Cl2, 293 K, scan rate:
0.1 Vsꢀ1): two reversible waves at E1/2 =0.4 and 0.64 V (cathodic adsorp-
tion, versus Cp*2Fe as an internal reference,[25] supporting electrolyte:
Figure 1. Zero-field Mçssbauer spectrum of complex 7a
which only shows the presence of pentamethylferricinium groups. Isomer
shift (I.S.): 0.6 mmsꢀ1 (vs. Fe); quadrupole splitting (Q.S.)=0 mmꢀ1
ACHTUGNTRNEN[UNG PF6]6 at 78 K,
.
0.1m [(nBu)4N]ACHTNGUTERNNU[G PF6]).
8916
www.chemeurj.org
ꢁ 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2013, 19, 8913 – 8921

Robust Ferricinium and Class-II Mixed-Valence Dendrimers
FULL PAPER
Scheme 4. Convergent synthesis of rigid ferrocenyl-terminated G2 dendron and dendrimer.
yielding compound 8a. Then, lengthening the tether at the
focal point in compound 9a is necessary to avoid excess
steric bulk in the final convergent assembly step of this
tetra-iron-sandwich dendron onto an arene core. Thus, the
reaction of dendron 8a with para-(bromo)trimethylsilylethy-
nylbenzene, followed by deprotection, yielded dendron 9a,
which showed longer focal points that were terminated by
an ethynyl group (Scheme 4).
metry and contained 12 pentamethylferrocenyl groups
(Scheme 4). Dendrimer 10a was characterized by 1H and
13C NMR spectroscopy, MS (MALDI-TOF), and elemental
analysis (see the Supporting Information).
The cyclic voltammogram (CV) of dodeca(pentamethyl-
ferrocenyl) metallodendrimer 10a (Figure 4) shows a single
chemically and electrochemically reversible 12-electron
wave for the 12 pentamethylferrocenyl redox centers (with a
weak cathodic adsorption), even with perfluorinated salt
Sonogashira reactions of dendron 9a with 1,3,5-triiodo-
benzene yielded stiff dendrimer 10a, which showed C3 sym-
NaACHTGNURTNEUNNG 3ACHUTGNERNN{UG 3,5-CAHTUNGTNER(NUG CF3)2}4) as the supporting elec-
[BArF ] (ArF =C6H
4
Chem. Eur. J. 2013, 19, 8913 – 8921
ꢁ 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
8917

D. Astruc et al.
well-defined, robust class-II mixed-valence ferricinium/ferro-
cenyl dendrimers.
The comparative influence of the inter-site distances be-
tween the six redox centers on the electrostatic effects of
hexa(Fc-ethynyl)benzene and hexa(Fc-ethynyl)-terminated
dendrimer 7b illustrates its crucial role in determining the
electrostatic effects and mixed-valence stabilization of iden-
tical ferrocenyl sites.
Two electron-transfer mechanisms in metallodendrimers
between the redox site and the electrode, that is, inter-site
hopping and fast rotation, have been suggested.[27] In rigid
metallodendrimers, the hopping mechanism is disfavored by
the inter-site distance, as confirmed by the absence of an
electrostatic effect. Thus, the fast-rotation mechanism
remains the most likely.
Figure 3. Zero-field Mçssbauer spectrum of complex 7cACHTNUGTRNEG[UN PF6]3 at and
78 K, which shows the presence of both ferrocenyl (I.S.=0.5 mmsꢀ1 vs.
Fe, Q.S.=2.4 mmsꢀ1) and pentamethylferrocenyl groups (I.S.=0.6 mmsꢀ1
vs. Fe, Q.S.=0 mmsꢀ1).
Experimental Section
General data: 1H NMR spectra were recorded at 258C on a Bruker AC
300 (300 MHz) spectrometer. 13C NMR spectra were recorded in pulsed
FT mode at 75.0 MHz on a Brucker AC 300 spectrometer. All chemical
shifts (d) are reported in parts per million (ppm) and are referenced to
Me4Si (TMS). Cyclic voltammetry (CV) measurements were recorded
under a nitrogen atmosphere in CH2Cl2, 208C, supporting electrolyte:
0.1m [nBu4N]ACTHNUGTRNENG[U PF6], working and counter electrodes: Pt, reference elec-
trode: Ag, internal reference: FeCp*2 (Cp*=h5-C5Me5),[25] scan rate:
0.200 Vsꢀ1. MS (MALDI-TOF) was performed by the CESAMO (Univ.
Bordeaux I, France) on a Voyager mass spectrometer (Applied Biosys-
tems). The instrument was equipped with a pulsed N2 laser (337 nm) and
a time-delayed extracted ion source. Spectra were recorded in positive-
ion mode by using the reflection at an accelerating voltage of 20 kV.
Samples were dissolved in CH2Cl2 at a concentration of 10 mgmLꢀ1. The
dithranol matrix solution was prepared by dissolving 10 mg in 1 mL of
CH2Cl2. The solution was combined in a 10:1 ratio (v/v) of the matrix to
the sample. 1–2 mL of the obtained solution was deposited onto the
sample target and vacuum-dried. Elemental analysis was performed at
the Center of Microanalyses of CNRS at Lyon Solaize (France).
Figure 4. CV of compound 10a (c=1 mm in CH2Cl2, 293 K, scan rate:
0.1 Vsꢀ1): reversible wave at E1/2 =0.42 V (versus decamethylferrocene as
an internal reference, supporting electrolyte: 0.1m [(nBu)4N]ACTHNUTRGNEUN[G PF6]).
trolyte. Interestingly, the 12 pentamethylferrocenyl groups
are oxidized in a single 12-electron wave, that is, the electro-
static effect is so weak that it is not observed, and the 12 dis-
tinct single redox potentials are so close to one another that
they are not distinguishable.[27] Moreover, the rigidity of this
metallodendrimer does not provide an adequate possibility
of electron hopping, which is postulated in the cases of the
ferrocenyl-terminated dendrimers with flexible tethers.
Thus, fast rotation of the dendrimer, which brings all of the
redox sites in turn into the vicinity of the electrode, appears
here to be the privileged mechanism for fast heterogeneous
electron transfer between all of these redox sites and the
electrode.[28]
Synthesis of 1,3-dibromo-5-(1,2,3,4,5-pentamethylferrocenylethynyl)ben-
zene) (8), 1-bromo-3,5-bis (pentamethylferrocenylethynyl)benzene (2a),
and 1,3,5-tris(pentamethylferrocenylethynyl)benzene: A mixture of cata-
lytic amounts of CuI (0.228 equiv, 1.26 mmol, 0.240 g), PdACHTUNGTRENNUNG(OAc)2
(0.213 equiv, 1.17 mmol, 0.263 g), and PPh3 (0.497 equiv, 2.74 mmol,
0.719 g) in diisopropylamine (100 mL) was stirred at 08C for 10 min.
Then, the mixture was treated with 1,2,3,4,5-pentamethyl-1’-ethynylferro-
cene (2 equiv, 11 mmol, 3.082 g)[21] and 1,3,5-tribromobenzene (1 equiv,
5.51 mmol, 1.734 g) and stirring was continued at 08C for 1 h, before
warming to RT and then heating at reflux for 2 h. After filtration and
evaporation to dryness, the residue was washed with dilute HCl, Na2CO3
(10%), and water and purified by column chromatography on silica gel
(pentane/CH2Cl2, 90:10). Successive bands of compounds 1 (0.417 g, 15%
yield), 2 (2 g, 50% yield), and 3 (0.150 g, 3% yield) were obtained as
solids after the removal of the solvent in vacuo.
Conclusions
1,3-Dibromo-5-(1,2,3,4,5-pentamethyl-ferrocenylethynyl)benzene
(8):
In conclusion, the synthetic strategies developed herein,
which involved selective bromide substitution in 1,3,5-tribro-
mobenzene, allowed the synthesis of the first stiff ferrocenyl,
ferricinium, and mixed-valence dendrimers. The introduc-
tion of only the permethylferrocenylethynyl group onto the
arene allowed the generation of robust all-ferricinium den-
drons and dendrimers upon oxidation. The alkynylation re-
actions selectivity provided unsymmetrical dendrons, thus
leading to the isolation and characterization of the first
1H NMR (300 MHz, CDCl3): d=1.88 (s, 15H; Cp*), 3.85–3.92 (d, 4H;
CH of Cp), 7.55 ppm (m, 3H; aromatic CH); 13C NMR (75 MHz,
CDCl3): d=10.3 (CH3), 64.8 (Cq of CpCH3), 73.3, 74.3 (CH of CpC C),
ꢁ
ꢁ
ꢁ
81.4 (Cq of CpC C), 83.5, 92.3 (C C), 122.7 (Cq of aromatic-Br), 127.9
ꢁ
(Cq of aromatic-C C), 132.5, 133.0 ppm (aromatic CH); elemental analy-
sis calcd (%) for C23H22Br2Fe: C 53.74, H 4.31; found: C 53.95, H 4.26.
1-Bromo-3,5-bis(pentamethylferrocenylethynyl)benzene (2a): 1H NMR
(300 MHz, CDCl3): d=1.91 (s, 30H; Cp*), 3.84–3.93 (d, 8H; CH of Cp),
7.53 ppm (m, 3H; aromatic CH); 13C NMR (75 MHz, CDCl3): d=10.6
ꢁ
(CH3Cp), 65.1 (Cq of CpCH3), 73.0, 74.1 (CH of CpC C), 81.2 (Cq of
8918
www.chemeurj.org
ꢁ 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2013, 19, 8913 – 8921

Robust Ferricinium and Class-II Mixed-Valence Dendrimers
FULL PAPER
ꢁ
ꢁ
CpC C), 84.2, 90.8 (C C), 121.9 (Cq of aromatic-Br), 126.3 (Cq of aro-
of aromatic); 13C NMR (75 MHz, CDCl3): d=10.7 (CH3), 64.3 (Cq of
ꢁ
ꢁ
ꢁ
matic-C C), 132.2, 132.5 ppm (CH of aromatic); elemental analysis calcd
CpCH3), 69.1, 70.0, 70.2, 73.1, 74.2 (CH of CpC C), 81.3 (Cq of CpC C),
ꢁ
(%) for C40H41BrFe2: C 67.35, H 5.79; found: C 67.24, H 5.65.
83.8, 84.2, 90.6, 91.0 (C C), 121.9 (Cq of aromatic-Br), 125.9,126.3 (Cq of
ꢁ
aromatic-C C), 132.3, 132.7 ppm (aromatic CH); elemental analysis
Synthesis of 1-ethynyl-3,5-bis(pentamethylferrocenylethynyl)benzene
(3a): To a mixture of compound 2a (2 g, 3.11 mmol) in dry triethylamine
calcd (%) for C35H31BrFe2: C 65.36, H 4.86; found: C 65.26, H 4.83.
(100 mL) were added [PdCl
(0.107 g, 18 mol%). The mixture was stirred at 508C and then trimethyl-
silylacetylene (0.9 mL, 6.22 mmol) was added. After 48 h, the same
amounts of [PdCl2ACHTUNGTRENNUNG(PPh3)2], CuI, and trimethylsilylacetylene were added
and the reaction mixture was stirred at 508C for 7 days. After evapora-
tion of the solvent, the crude reaction mixture was purified by column
chromatography on silica gel (CH2Cl2), thereby affording pure
1,3-bis(pentamethylferrocenylethynyl)-5-(trimethylsilylethynyl)benzene
(2a’, 2.18 g, 2.98 mmol, 96% yield; for the structure, see the Supporting
Information).
(PPh3)2] (0.218 g, 10 mol%) and CuI
1-(Pentamethylferrocenylethynyl)-3,5-bis(ferrocenyl-ethynyl)benzene:
1H NMR (300 MHz, CDCl3): d=1.86 (s, 15H; Cp*), 3.86–3.96 (d, 4H;
CH of C5H4FeCp*), 4.26 (m, 14H; CH of C5H4 and C5H5), 4.52- 4.53(m,
4H; CH of C5H4FeCp), 7.52–7.54 ppm (m, 3H; CH of aromatic);
13C NMR (75 MHz, CDCl3): d=10.5 (CH3), 64.5 (Cq of CpCH3), 68.8,
ꢁ
ꢁ
69.8, 71.3, 73.0, 74.2 (CH of CpC C), 81.2 (Cq of CpC C), 84.3, 84.7,
ꢁ
ꢁ
89.2, 89.5 (C C), 124.2, 124.7 (Cq of aromatic-C C), 132.5, 132.6 ppm
(aromatic CH); MS(MALDI-TOF): m/z calcd for C47H40Fe3: 772.376;
found: 772.18; elemental analysis calcd (%) for C47H40Fe3: C 73.09,
H 5.22; found: C73.47, H 5.26.
Complex 2a’ (2.18 g, 2.98 mmol) was dissolved in THF (25 mL) and
MeOH (25 mL). Then, K2CO3 (0.824 g, 5.96 mmol) was added and the
mixture was stirred at RT for 30 min. The reaction was quenched with a
saturated aqueous solution of ammonium chloride and the product was
extracted with CH2Cl2. The combined organic layers were dried over
Na2SO4. After evaporation of the solvent, complex 4 (1.88 g, 2.86 mmol,
96% yield) was obtained.
Synthesis of 1-ethynyl-3-(pentamethylferrocenylethynyl)-5-(ferrocenyle-
thynyl)benzene (3c): To a mixture of compound 2c (3.867 g, 6.01 mmol)
in dry triethylamine (100 mL) were added [PdCl2ACHTNUGTRENUNG(PPh3)2] (0.422 g,
10 mol%) and CuI (0.206 g, 18 mol%). The mixture was stirred at 508C
and trimethylsilylacetylene (1.7 mL, 12.02 mmol) was added. After 48 h,
the same amounts of [PdCl2ACTHNUTRGNEUNG(PPh3)2], CuI, and trimethylsilylacetylene
were added and the reaction mixture was stirred at 508C for 7 days.
After evaporation of the solvent, the crude reaction mixture was purified
by column chromatography on silica gel (CH2Cl2), thereby leading to
pure complex 2c’ (3.811 g, 5.77 mmol, 96% yield).
1-ethynyl-3,5-bis(pentamethylferrocenylethynyl)benzene (3a): 1H NMR
ꢁ
(300 MHz, CDCl3): d=1.87 (s, 30H; Cp*), 3.14 (s, 1H; CH C), 3.89–4.0
(d, 8H; CH of Cp), 7.55–7.60 ppm (d, 3H; CH of aromatic). 13C NMR
(75 MHz, CDCl3): d=10.7 (CH3), 66.0 (Cq of CpCH3), 73.5, 74.6 (CH of
Complex 2c’ (3.811 g, 5.77 mmol) was dissolved in THF (50 mL) and
MeOH (50 mL). Then, K2CO3 (1.595 g, 11.54 mmol) was added and the
mixture was stirred at RT for 30 min. The reaction was quenched with a
saturated aqueous solution of ammonium chloride and the product was
extracted with CH2Cl2. The combined organic layers were dried over
Na2SO4. After evaporation of the solvent, compound 3c (3.259 g,
5.54 mmol, 96% yield) was obtained.
ꢁ
ꢁ
ꢁ
ꢁ
CpC C), 78.0 (CH C), 81.6 (Cq of CpC C), 82.5 (C CH), 84.7, 90.1
ꢁ
ꢁ
ꢁ
(C C), 122.7 (Cq of aromatic-C CH), 125.1 (Cq of aromatic-C C),
133.4, 133.9 ppm (CH of aromatic); MS (MALDI-TOF): m/z calcd for
C42H42Fe2: 658.49; found: 658.20; elemental analysis calcd (%) for
C42H42Fe2: C 76.61, H 6.43; found: C 76.61, H 6.55.
Synthesis of complex 7a: A mixture of 1,3,5-triiodobenzene (0.100 g,
0.219 mmol, 1 equiv), 1-ethynyl-3,5-bis(pentamethylferrocenylethynyl)-
benzene (3a, 0.476 g, 0.723 mmol, 3.3 equiv), [(PPh3)2PdCl2] (0.009 g,
0.013 mmol, 0.06 equiv), and cuprous iodine (0.037 g, 0.197 mmol,
0.9 equiv) in triethylamine (10 mL) was magnetically stirred in a Schlenk
flask overnight at 508C. The solvent was evaporated, and the residue was
dissolved in CH2Cl2. The organic phase was washed with water and dried
with sodium sulfate, the solvent was removed under vacuum, and the
crude reaction mixture was purified by column chromatography on silica
gel (pentane/CH2Cl2, 70:30), thereby affording compound 7a (0.284 g,
0.118 mmol, 54% yield). 1H NMR (300 MHz, CDCl3): d=1.81 (s, 90H;
Cp*), 3.89–4.0 (d, 24H; CH of Cp), 7.55–7.70 ppm (d, 12H; CH of aro-
matic); 13C NMR (75 MHz, CDCl3): d=10.9 (CH3), 65.7 (Cq of CpCH3),
1-Ethynyl-3-(pentamethylferrocenylethynyl)-5-(ferrocenylethynyl)benzene
(3c): 1H NMR (300 MHz, CDCl3): d=1.94 (s, 15H; Cp*), 3.16 (s, 1H;
ꢁ
CH C), 3.87–3.97 (d, 4H; CH of C5H4FeCp*), 4.30 (s, 7H; CH of C5H4
and C5H5), 4.56–4.57 (m, 2H; CH of C5H4FeCp), 7.59–7.64 ppm (m; 3H,
CH of aromatic); 13C NMR (75 MHz, CDCl3): d=10.8 (CH3), 64.6 (Cq of
ꢁ
ꢁ
CpCH3), 69.2, 70.1, 71.6, 73.1, 74.3 (CH of CpC C), 78.2 (CH C), 81.3
ꢁ
ꢁ
(Cq of CpC C), 82.5, 83.8, 84.2, 90.6, 91.0 (C C), 122.8, 124.8, 125.2 (Cq
ꢁ
of aromatic-C C), 133.5, 134.0 ppm (aromatic CH); MS (MALDI-TOF):
m/z calcd for C37H32Fe2: 588.355; found: 588.0; elemental analysis calcd
(%) for C37H32Fe2: C 75.53, H 5.48; found: C 75.19, H 5.31.
Synthesis of complex 7c: A mixture of 1,3,5-triiodobenzene (0.100 g,
0.219 mmol, 1 equiv), 1-ethynyl-3-(pentamethylferrocenylethynyl)-5-(fer-
ꢁ
ꢁ
73.2, 74.4 (CH of CpC C), 81.4 (Cq of CpC C), 84.8, 88.4, 89.7, 90.1
rocenyl-ethynyl)benzene
(3c,
0.425 g,
0.723 mmol,
3.3 equiv),
ꢁ
ꢁ
ACHTUNGTRENNUNG(C C), 123.4, 123.9, 125.2, 122.7 (Cq of aromatic-C C), 132.9, 133.8,
[(PPh3)2PdCl2] (0.009 g, 0.013 mmol, 0.06 equiv), and cuprous iodine
(0.037 g, 0.197 mmol, 0.9 equiv) in triethylamine (10 mL) was magnetical-
ly stirred in a Schlenk flask overnight at 508C. The solvent was evaporat-
ed under vacuum and the residue was dissolved in CH2Cl2. The organic
phase was washed with water and dried with sodium sulfate, the solvent
was removed under vacuum, and the crude reaction mixture was purified
by column chromatography on silica gel (pentane/CH2Cl2, 70:30), thereby
leading to product 7c (0.226 g, 0.123 mmol, 56% yield). 1H NMR
(300 MHz, CDCl3): d=1.91 (s, 45H; Cp*), 3.83–3.93 (d, 12H; CH of
C5H4FeCp*), 4.26 (s, 21H; CH of C5H4 and C5H5), 4.53 (s, 6H; CH of
C5H4FeCp), 7.58–7.69 ppm (d, 12H; aromatic CH); 13C NMR (75 MHz,
CDCl3): d=10.7 (CH3), 64.6 (Cq of CpCH3), 69.1, 70.1, 71.6, 73.7, 74.7
134.5 ppm (CH of aromatic); MS (MALDI-TOF): m/z calcd for
C132H126Fe6: 2407.534; found: 2047.7; elemental analysis calcd (%) for
C132H126Fe6: C 77.43, H 6.20; found: C 77.24, H 6.58; CV (CH2Cl2, 293 K):
one reversible wave E1/2 =0.4 V (versus decamethylferrocene, supporting
electrolyte: 0.1m [(nBu)4N]ACTHNUTRGNEUN[G PF6]).
Synthesis of 1-bromo-3-(pentamethylferrocenylethynyl)-5-(ferrocenyle-
thynyl)benzene (2c) and 1-(pentamethylferrocenylethynyl)-3,5-bis(ferro-
cenylethynyl)benzene: A mixture of catalytic amounts of CuI (0.06 equiv,
0.6 mmol, 0.114 g), PdACHTUNGTRENNUNG(OAc)2 (0.06 equiv, 0.6 mmol, 0.135 g), and PPh3
(0.122 equiv 1.22 mmol, 0.320 g) in diisopropylamine (100 mL) was stir-
red at 08C for 10 min. Then, the mixture was treated with ethynylferro-
cene (1 equiv 10 mmol, 2.101 g) and 1,3-dibromo-5-(pentamethylferroce-
nylethynyl)benzene (8, 1 equiv, 10 mmol, 5.141 g) and stirring was contin-
ued at 08C for 1 h before warming to RT and heating at reflux for 2 h.
After filtration and evaporation to dryness, the residue was washed with
dilute HCl, Na2CO3 (10%), and water and purified by column chroma-
tography on silica gel with pentane/CH2Cl2 (90:10) to afford compound 6
(3.867 g, 60% yield) and then with pentane/CH2Cl2 (80:20) to afford
compound 7 (0.532 g, 7% yield).
ꢁ
ꢁ
(CH of CpC C), 81.3 (Cq of CpC C), 84.4, 84.8, 88.5, 89.6, 89.9, 90.2
ꢁ
ꢁ
(C C), 123.3, 123.9, 124.8, 125.2 (Cq of aromatic-C C), 133.0, 133.2,
133.8, 134.4 ppm (aromatic CH); MS (MALDI-TOF): m/z calcd for
C117H96Fe6: 1837.131; found: 1837.2; elemental analysis calcd (%) for
C117H96Fe6: C 76.49, H 5.27; found: C 76.72, H 5.48. CV (CH2Cl2, 293 K):
two reversible waves E1/2 =0.4, 0.64 V (versus decamethylferrocene; sup-
porting electrolyte [(nBu)4N]PF6).
Synthesis of complexes 6 and 11a: A mixture of catalytic amounts of CuI
(0.09 equiv, 0.089 mmol, 0.017 g), PdACTHUGNTERNNU(G OAc)2 (0.075 equiv, 0.074 mmol,
0.017 g), and PPh3 (0.183 equiv 0.180 mmol, 0.047 g) in diisopropylamine
(50 mL) was stirred at 08C for 10 min. Then, the mixture was treated
Complex 2c: 1H NMR (300 MHz, CDCl3): d=1.90 (s, 15H; Cp*), 3.85–
3.94 (d, 4H; CH of C5H4FeCp*), 4.27–4.29 (m, 7H; CH of C5H4 and
C5H5), 4.52–4.54 (m, 2H; CH of C5H4FeCp), 7.53–7.57 ppm (m, 3H; CH
Chem. Eur. J. 2013, 19, 8913 – 8921
ꢁ 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
8919

D. Astruc et al.
[PF6]3: IR (KBr): n˜ =2213.52 (C C), 840.76 cm (PF6ꢀ); ele-
ꢀ1
ꢁ
with
1-ethynyl-3,5-bis(pentamethylferrocenylethynyl)benzene
(3a,
Complex 7c
mental analysis calcd (%) for C117H96F18Fe6P3: C 61.85, H 4.26; found:
C 61.45, H 4.30.
2 equiv 1.97 mmol, 1.30 g) and 1,3,5-tribromobenzene (1 equiv,
0.985 mmol, 0.310 g) and stirring was continued at 08C for 1 h before
warming to RT and heating at reflux for 2 h. After filtration and evapora-
tion to dryness, the residue was washed with dilute HCl, Na2CO3 (10%),
and water and purified by column chromatography on silica gel with pen-
tane/CH2Cl2 (90:10) to afford compound 6 (137 mg, 15% yield) and then
with pentane/CH2Cl2 (80:20) to afford compound 11a (700 mg, 48%
yield).
Acknowledgements
Complex 6: 1H NMR (300 MHz, CDCl3): d=1.87 (s, 30H; Cp*), 3.88–
3.98 (d, 8H; CH of Cp), 7.54–7.66 ppm (m, 6H; aromatic CH); 13C NMR
(75 MHz, CDCl3): d=10.7 (CH3), 66.4 (Cq of CpCH3), 73.9, 74.8 (CH of
Assistance for the Mçssbauer spectroscopy from Dr. Lionel Salmon
(Laboratoire de Chimie de Coordination, Toulouse) and financial sup-
port from the Universitꢀ Bordeaux 1, the Centre National de la Recher-
che Scientifique, and the Agence Nationale pour la Recherche (PhD
grant to A.K.D.) are gratefully acknowledged.
ꢁ
ꢁ
ꢁ
CpC C), 81.8 (Cq of CpC C), 84.6, 87.0, 90.2, 90.8 (C C), 122.7, 125.2,
ꢁ
126.4 (Cq of aromatic-C C and aromatic-Br), 132.8, 133.1, 134.0,
134.2 ppm (aromatic CH); MS (MALDI-TOF): m/z calcd for C48H44Fe2:
892.379; found: 892.2; elemental analysis calcd (%) for C48H44Fe2:
C 64.61, H 4.97; found: C 64.25, H 5.43.
[1] a) R. Rulkens, A.-J. Lough, I. Manners, S. R. Lovelace, C. Grant,
W. E. Geiger, J. Am. Chem. Soc. 1996, 118, 12683–12695; b) G. R.
Whittell, I. Manners, Adv. Mater. 2007, 19, 3439–3468.
[2] a) V. Balzani, F. Barrigelletti, S. Campagna, G. Denti, A. Juris, S.
Serroni, M. Venturi, Acc. Chem. Res. 1998, 31, 26–34; b) G. R. New-
kome, E. He, C. N. Moorefield, Chem. Rev. 1999, 99, 1689–1746;
c) P. Ceroni, G. Bergamini, F. Marchioni, V. Balzani, Prog. Polym.
Sci. 2005, 30, 453–473; d) D. Astruc, E. Boisselier, C. Ornelas,
Chem. Rev. 2010, 110, 1857–1959.
[3] a) R. M. Crooks, M. Zhao, L. Sun, V. Chechik, L. K. Yeung, Acc.
Chem. Res. 2001, 34, 181–190; b) Nanoparticles. From Theory to
Application, Wiley-VCH, Weinheim, 2004; c) M.-C. Daniel, D.
Astruc, Chem. Rev. 2004, 104, 293–346.
Complex 11a: 1H NMR (300 MHz, CDCl3): d=1.93 (s, 60H; Cp*), 3.90-
4.01 (d, 16H; CH of Cp), 7.62–7.73 ppm (m, 9H; CH of aromatic);
13C NMR (75 MHz, CDCl3): d=10.5 (CH3), 65.2 (Cq of CpCH3), 72.8,
ꢁ
ꢁ
ꢁ
74.0 (CH of CpC C), 81.1 (Cq of CpC C), 84.6, 87.5, 90.0 (C C), 121.8,
ꢁ
122.9, 125.0 (Cq of aromatic-C C and aromatic-Br), 132.6, 133.3, 133.6,
134.0 ppm (aromatic CH); MS (MALDI-TOF): m/z calcd for C90H85Fe4:
1469.957; found: 1470.5; elemental analysis calcd (%) for C90H85Fe4:
C 73.54, H 5.83; found: C 73.40, H 6.13.
Complex 9a: Same procedure as for 3c; 1H NMR (300 MHz, CDCl3):
ꢁ
d=1.89 (s, 60H; Cp*), 3.25 (s, 1H; CH C), 3.93- 4.05 (d, 16H; CH of
Cp), 7.55–7.77 ppm (m, 13H; aromatic CH); 13C NMR (75 MHz, CDCl3):
ꢁ
[4] a) Electron Transfer in Chemistry, (Ed.: V. Balzani), Vol. 1–4,
Wiley-VCH, Weinheim, 2001; b) W. E. Geiger, Organometallics
2007, 26, 5738–5765; c) H. B. Gray, J. R. Winkler, Biochim. Biophys.
Acta Bioenerg. 2010, 1797, 1563–1572.
[5] a) W. Tian, S. Datta, S. Hong, R. Reifenberger, J. Henderson, C. P.
Kubiak, J. Chem. Phys. 1998, 109, 2874–2882; b) R. Kato, Chem.
Rev. 2004, 104, 5319; c) Organic Conductors, Semiconductors and
Magnets: From Synthesis to Molecular Electronics, (Eds.: L.
Ouahab, E. Yagubskii), NATO Sci. Ser., Vol. 139, Kluwer, Dor-
drecht, 2004.
[6] a) M. B. Robin, P. Day, Inorg. Chem. Radiochem. 1967, 9, 247–422;
b) D. E. Richardson, H. Taube, Coord. Chem. Rev. 1984, 60, 107–
129; c) D. Astruc, Acc. Chem. Res. 1997, 30, 383–391; d) N. S. Hush,
Ann. N. Y. Acad. Sci. 2003, 1006, 1–20.
[7] a) R. W. J. Scott, O. M. Wilson, R. M. Crooks, J. Phys. Chem. B
2005, 109, 692–704; b) B. D. Chandler, J. D. Gilbertson, Top. Orga-
nomet. Chem. 2006, 20, 97–120; c) D. Astruc, K. Heuze, S. Gatard,
D. Mꢀry, S. Nlate, Adv. Synth. Catal. 2005, 347, 329–338.
[8] a) P. D. Beer, P. A. Gale, Angew. Chem. 2001, 113, 502–532; Angew.
Chem. Int. Ed. 2001, 40, 486–516; b) U. Drechsler, B. Erdogan,
V. M. Rotello, Chem. Eur. J. 2004, 10, 5570–5579; c) C. M. Casado,
B. Alonso, J. Losada, M. P. Garcia-Armada in Designing Dendrim-
ers, (Eds.: S. Campagna, P. Ceroni, F. Puntoriero), Wiley-VCH,
Weinheim, 2012, pp. 219–262.
[9] For reviews on ferrocenyl dendrimers and their electrochemical
properties, see: a) C. M. Casado, I. Cuadrado, M. Morꢃn, B. Alonso,
B. Garcia, B. Gonzales, J. Losada, Coord. Chem. Rev. 1999, 185–
186, 53–79; b) C. M. Casado, M. Morꢃn, B. Alonso, M. Barranco, J.
Losada, Appl. Organomet. Chem. 1999, 13, 245–259; c) S. H.
Hwang, C. D. Shreiner, C. N. Moorefield, G. N. Newkome, New J.
Chem. 2007, 31, 1192.
d=10.8 (CH3), 66.1 (Cq of CpCH3), 73.6, 74.7 (CH of CpC C), 79.4
ꢁ
ꢁ
ꢁ
(CH C), 81.6 (Cq of CpC C), 83.3, 84.8, 88.5, 89.7, 90.3 (C C), 122.5,
ꢁ
123.4, 124.0, 125.3 (Cq of aromatic-C C), 131.7, 132.2, 132.9, 133.8,
134.4 ppm (aromatic CH); MS (MALDI-TOF): m/z calcd for C100H90Fe4:
1515.203; found: 1515.8. elemental analysis calcd (%) for C100H90Fe4:
C 79.27, H 5.99; found: C 79.40, H 6.15.
Synthesis of complex 10a: A mixture of 1,3,5-triiodobenzene (0.05 g,
0.110 mmol, 1 equiv), compound 9a (0.550 g, 0.363 mmol, 3.3 equiv),
[(PPh3)2PdCl2] (0.005 g, 6.6ꢂ10ꢀ3 mmol, 0.06 equiv), cuprous iodine
(0.019 g, 9.9ꢂ10ꢀ2 mmol, 0.9 equiv) and triethylamine (10 mL) was mag-
netically stirred in a Schlenk flask overnight at 508C. The solvent was
evaporated under vacuum and the residue was dissolved in CH2Cl2. The
organic phase was washed with water and dried with sodium sulfate, the
solvent was removed under vacuum, and the crude reaction mixture was
purified by column chromatography on silica gel (pentane/CH2Cl2, 60:40)
1
to afford compound 10a (0.173 g, 3.74ꢂ10ꢀ2 mmol, 34% yield). H NMR
(300 MHz, CDCl3): d=1.86 (s, 3ꢂ60H; Cp*), 3.87–3.98 (d, 3ꢂ14H; CH
of C5H4FeCp*), 7.54–7.70 ppm (d, 12H; aromatic CH); 13C NMR
(75 MHz, CDCl3): d=10.8 (CH3), 66.1 (Cq of CpCH3), 73.6, 74.7 (CH of
CpC C), 81.6 (Cq of CpC C), 84.8, 88.5, 89.7, 90.3 (C C), 122.5, 123.4,
124.0, 125.3 (Cq of aromatic-C C), 131.7, 132.2, 132.9, 133.8, 134.4 ppm
(aromatic CH); MS (MALDI-TOF): m/z calcd for C306H270Fe12: 4617.558;
found: 4617.3; elemental analysis calcd (%) for C306H270Fe12: C 77.89,
H 7.90; found: C 77.25, H 7.70; CV (CH2Cl2, 293 K): one reversible wave
ꢁ
ꢁ
ꢁ
ꢁ
E
1/2 =0.42 V (versus decamethylferrocene, supporting electrolyte
[(nBu)4N]PF6).
Synthesis of complexes 7a
N
ACHTUGNTRENUN[GN PF6]3: Compound 7a (75 mg,
3.66ꢂ10ꢀ2 mmol) and Cp2Fe+PF6 (72.82 mg, 0.22 mmol, 6 equiv) were
stirred in freshly distilled and degassed CH2Cl2 (20 mL). After evapora-
tion of the solvent in vacuo and washing with diethyl ether (3ꢂ20 mL),
[10] a) Z. Xu, J. S. Moore, Angew. Chem. 1993, 105, 261–264; Angew.
Chem. Int. Ed. Engl. 1993, 32, 246–248; b) P. Bhyrappa, J. K.
Young, J. S. Moore, K. S. Suslick, J. Am. Chem. Soc. 1996, 118,
5708–5711; c) J. S. Moore, Acc. Chem. Res. 1997, 30, 402–413.
[11] a) S. Campagna, G. Denti, S. Serroni, M. Ciano, V. Balzani, Inorg.
Chem. 1991, 30, 3728–3732; b) V. Balzani, P. Ceroni, A. Juris, M.
Venturi, S. Campagna, F. Puntoriero, S. Serroni, Coord. Chem. Rev.
2001, 219–221, 545–572; c) V. Balzani, G. Bergamini, P. Ceroni, F.
Vçgtle, Coord. Chem. Rev. 2007, 251, 525–535.
complex 7aACHTUNGTRENNUNG[PF6]6 (85.42 mg, 80% yield) was obtained as a dark-green
ꢀ
salt. The same procedure was used with compound 7c and Cp2Fe+PF6
(3 equiv) to obtain complex 7c
ACHTUGNTERN[NUNG PF6]3.
ꢁ
Complex 7a
[PF6]6: IR (KBr): n˜ =2219.82 (C C), 836.96 cmꢀ1 (PF6ꢀ); ele-
mental analysis calcd (%) for C132H126F36Fe6P6·H2O: C 54.01, H 4.39;
found: C 53.84, H 4.40. For the UV/Vis spectra of compounds 7a and 7a-
A
ACHTUGNERTN[NUNG PF6]6, see
8920
www.chemeurj.org
ꢁ 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2013, 19, 8913 – 8921

Robust Ferricinium and Class-II Mixed-Valence Dendrimers
FULL PAPER
[12] a) S. Setayesh, A. C. Grimsdale, T. Weil, V. Enkelmann, K. Mꢄllen,
F. Meghdadi, E. J. W. List, G. Leising, J. Am. Chem. Soc. 2001, 123,
946–953; b) R. E. Bauer, A. C. Grimsdale, K. Mꢄllen, Top. Curr.
Chem. 2005, 245, 253–286; c) M. Yin, J. Shen, G. O. Pfugfeder, K.
Mꢄllen, J. Am. Chem. Soc. 2008, 130, 7806–7807.
[20] a) P. Jutzi, B. Kleinebekel, J. Organomet. Chem. 1997, 545–546,
573–576; b) H. Fink, N. J. Long, A. J. Martin, G. Opromolla, A. J. P.
White, D. J. Williams, P. Zanello, Organometallics 1997, 16, 2646–
2650.
[21] B. Bildstein, A. Hradsky, H. Kopacka, R. Malleier, K.-H. Ongania,
J. Organomet. Chem. 1997, 540, 127–145.
[13] a) A. M. McDonagh, M. G. Humphrey, M. Samoc, B. Luther-Davies,
Organometallics 1999, 18, 5195–5197; b) S. K. Hurst, M. P. Ci-
fuentes, M. G. Humphrey, Organometallics 2002, 21, 2353–2355;
c) A. M. McDonagh, C. E. Powell, J. P. Morrall, M. G. Humphrey,
Organometallics 2003, 22, 1402–1413; d) C. E. Powell, J. P. Morrall,
S. A. Ward, M. P. Cifuentes, E. G. A. Otaras, M. Samoc, M. G. Hum-
phrey, J. Am. Chem. Soc. 2004, 126, 12234–12235; e) C. E. Powell,
S. K. Hurst, J. P. Morrall, M. P. Cifuentes, R. L. Roberts, M. Samoc,
M. G. Humphrey, Organometallics 2007, 26, 4456–4463; f) M. G.
Humphrey, J. P. Morrall, G. T. Dalton, M. P. Cifuentes, M. G. Hum-
phrey, Angew. Chem. 2007, 119, 276; Angew. Chem. Int. Ed. 2007,
46, 272; g) K. A. Green, M. P. Cifuentes, M. Samoc, M. G. Hum-
phrey, Coord. Chem. Rev. 2011, 255, 2025–2038; h) K. A. Green,
M. P. Cifuentes, M. Samoc, M. G. Humphrey, Coord. Chem. Rev.
2011, 255, 2530–2541.
[22] For flexible pentamethylferrocenyl dendrimers, see: a) M.-C.
Daniel, J. Ruiz, J.-C. Blais, N. Daro, D. Astruc, Chem. Eur. J. 2003,
9, 4371–4379; b) C. Ornelas, J. Ruiz, C. Belin, D. Astruc, J. Am.
Chem. Soc. 2009, 131, 590–601; for flexible octamethylferrocenyl
dendrimers, see: c) M. P. Garcia-Armada, J. Losada, M. Zamora, B.
Alonso, I. Cuadrado, C. M. Casado, Bioelectrochem. 2006, 69, 65–
73; d) J. Losada, M. Zamora, P. Garcia-Armada, I. Cuadrado, B.
Alonso, C. M. Casado, Anal. Bioanal. Chem. 2006, 385, 1209–1217;
e) M. Zamora, S. Herrero, J. Losada, I. Cuadrado, B. Alonso, C. M.
Casado, Organometallics 2007, 26, 2688–2693.
[23] a) N. Camine, U. T. Mueller-Westerhoff, W. E. Geiger, J. Organomet.
Chem. 2001, 637, 823–826; b) F. Barriꢅre, N. Camine, W. E. Geiger,
J. Am. Chem. Soc. 2002, 124, 7262–7263; c) F. Barriꢅre, W. E.
Geiger, J. Am. Chem. Soc. 2006, 128, 3980–3989; d) W. E. Geiger, F.
Barriꢅre, Acc. Chem. Res. 2010, 43, 1030–1039.
[14] Y. Ochi, M. Suzuki, T. Imaoka, M. Murata, H. Nishihara, Y. Einaga,
K. Yamamoto, J. Am. Chem. Soc. 2010, 132, 5061–5069.
[24] R. L. Collins, J. Chem. Phys. 1965, 42, 1072–1074.
[25] J. Ruiz, D. Astruc, C. R. Acad. Sci. Sꢀr. IIc 1998, 1, 21–27.
[26] I. Cuadrado, C.-M. Casado, B. Alonso, M. Morꢃn, J. Losada, V.
Belsky, J. Am. Chem. Soc. 1997, 119, 7613–7614.
[27] a) J. B. Flanagan, S. Margel, A. Bard, J. Am. Chem. Soc. 1978, 100,
4248–4253; b) J. E. Sutton, P. M. Sutton, H. Taube, Inorg. Chem.
1979, 18, 1017–1024.
[28] a) S. J. Green, J. J. Pietron, J. J. Stokes, M. J. Hostetler, H. Wu, W. P.
Wuelfing, R. W. Murray, Langmuir 1998, 14, 5612–5619; b) C. B.
Gorman, B. L. Smith, H. Parkhurst, H. Sierputowska-Gracz, C. A.
Haney, J. Am. Chem. Soc. 1999, 121, 9958; c) C. Amatore, Y.
Bouret, E. Maisonhaute, J. I. Goldsmith, H. D. AbruÇa, Chem. Eur.
J. 2001, 7, 2206–2226; d) F. Hauquier, J. Ghilane, B. Fabre, P.
Hapiot, J. Am. Chem. Soc. 2008, 130, 2748–2749; e) D. Astruc, Nat.
Chem. 2012, 4, 255–267.
[15] a) Y. Yu, A. D. Bond, P. W. Leonard, U. J. Lorenz, T. V. Timofeeva,
K. P. C. Vollhardt, D. W. Glenn, A. A. Yakovenko, Chem. Commun.
2006, 2572–2574; b) R. Diercks, J. C. Armstrong, R. Boese, K. P. C.
Vollhardt, Angew. Chem. 1986, 98, 270–271; Angew. Chem. Int. Ed.
Engl. 1986, 25, 268–269; c) R. Boese, J. R. Green, J. Mittendorf,
K. P. C. Vollhardt, Angew. Chem. 1992, 104, 1643–1645; Angew.
Chem. Int. Ed. Engl. 1992, 31, 314.
[16] a) A. K. Diallo, J.-C. Daran, F. Varret, J. Ruiz, D. Astruc, Angew.
Chem. 2009, 121, 3187–3191; Angew. Chem. Int. Ed. 2009, 48, 3141–
3145; b) A. K. Diallo, J.-C. Daran, F. Varret, J. Ruiz, D. Astruc, J.
Am. Chem. Soc. 2011, 133, 629–641.
[17] G. R. Newkome, C. D. Shreiner, Polymer 2008, 49, 1–173.
[18] K. Sonogashira, Y. Tohda, N. Hagihara, Tetrahedron 1975, 31, 4467.
[19] E. Negishi, Z. Huang, G. Huang, S. Mohan, C. Wang, H. Hattori,
Acc. Chem. Res. 2008, 41, 1474–1485.
Received: February 12, 2013
Published online: May 21, 2013
Chem. Eur. J. 2013, 19, 8913 – 8921
ꢁ 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
8921