Click chemistry of an ethynylarene iron complex: Syntheses, properties, and redox chemistry of cationic bimetallic and dendritic iron-sandwich complexes

Article abstract of DOI:10.1021/om500495r

The functionalization of dendrimers and other macromolecules with cationic redox-active organometallics remains a target toward metal-containing dendrimers and polymers that can serve in particular as polyelectrolytes and multielectron redox reagents. Alo

Full text of DOI:10.1021/om500495r

Article
pubs.acs.org/Organometallics
Click Chemistry of an Ethynylarene Iron Complex: Syntheses,
Properties, and Redox Chemistry of Cationic Bimetallic and Dendritic
Iron-Sandwich Complexes
Amalia Rapakousiou, Yanlan Wang, Roberto Ciganda, Jean-Michel Lasnier, and Didier Astruc*
ISM, UMR CNRS 5255, University of Bordeaux, 33405 Talence Cedex, France
S
* Supporting Information
ABSTRACT: The functionalization of dendrimers and other
macromolecules with cationic redox-active organometallics
remains a target toward metal-containing dendrimers and
polymers that can serve in particular as polyelectrolytes and
multielectron redox reagents. Along this line, we report the click
functionalization of organometallics and dendrimers with a
redox-active ethynylarene iron complex, [FeCp(η6-
ethynylmesitylene)][PF6], 3, easily available from [FeCp(η6-
mesitylene)][PF6], 1. Complex 3 reacts with azidomethylferro-
cene upon catalysis by copper sulfate and sodium ascorbate
(CuAAC reaction) to give a bimetallic complex that is reduced
on the mesitylene ligand to a mixture of isomeric cyclo-
hexadienyl complexes. Complex 3 also reacts according to the
same click reaction with zeroth- and first-generation metallodendrimers containing, respectively, 9 and 27 azido termini to
provide new polar polycationic metallodendrimers that are reversibly reduced, on the electrochemical time scale, to 19-electron
FeI species.
Scheme 1. Basic Chemistry of Complex 1
INTRODUCTION
■
Metallodendrimers are a rich chemistry1 that finds applications
in catalysis,2 sensing,3 molecular electronics,4 and other
molecular materials properties.1 Metallocene-terminated den-
drimers occupy a large part of this chemistry because of their
rich redox properties that are especially developed and applied
with ferrocene dendrimers.5 Very few polycationic dendrimers
are known, almost exclusively cobalticenium dendrimers,6,7
however, despite their polyelectrolyte properties. The chemistry
of the family of complexes [FeCp(η6-arene)][PF6]8 (Cp = η5-
C5H5) parallels that of cobalticenium9 and is also quite rich. For
instance, the basic properties of the readily available complex
[FeCp(η6-mesitylene)][PF6], 1,10 are illustrated in Scheme 1.
Further functionalization of 1 was thus a target in order to graft
this cheap and easily available cationic and redox-active
organoiron complex onto the periphery of dendrimers.
Recently, it has been possible to nearly quantitatively
functionalize complex 1 by the introduction of an ethynyl
group on the arene ligand upon addition of the ethynyl
carbanion in the form of lithium acetylideethylenediamine in
THF giving exo-cyclohexadienyl adduct 2, followed by removal
of the endo hydride using commercial trityl hexafluorophos-
phate providing the ethynyl-substituted arene complex [FeCp-
(η6-ethynylmesitylene)][PF6], 3 (Scheme 2).11
This procedure is an extension of the very useful analogous
functionalization of cobalticenium.12 Complex 3 that is readily
obtained in this way serves in further functionalization. For
instance, the new facile hydroamination of this complex 2 leads
Received: May 9, 2014
© XXXX American Chemical Society
A
dx.doi.org/10.1021/om500495r | Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
the oxidation of the ferrocenyl fragment to the 17-electron
ferricenium species, and the reduction wave at −1.36 V vs
[FeCp*2]+/0 is due to the reduction of the triazolyl-[FeIICp(η6-
C6H2Me3-)]PF6 fragment to its 19-electron FeI isostructural
analogue.8b Both waves show electrochemical and chemical
reversibility under N2 indicating the robustness of compound 5
and the triazolyl group attached to the [FeIICp(η6-C6H2Me3‑)]-
PF6 sandwich under these conditions. When the CV is recorded
under air, the situation changes, however. The reduction wave
of triazolyl-[FeIICp(η6-C6H2Me3-)]PF6 is then irreversible with
a potential Ep of −1.34 V vs [FeCp*2]+/0, whereas remarkably a
new irreversible oxidation wave appeared at −0.68 V vs
[FeCp*2]+/0. It is known that the 19-electron complex [FeII(η5-
Cp)(η6-C6Me6)] is extremely reactive toward O2, reacting with
an overall H atom abstraction from a benzylic methyl
substituent according to a mechanism that comprises electron
transfer from FeI to O2 followed by deprotonation by
Scheme 2. Synthesis of Ethynyl Derivative 3
to the formation of conjugated trans-enamines,11 but attempts
to extend this functionalization to dendritic amines were
unsuccessful, although such an extension worked well with
ethynylcobalticenium.13 However, we report here the successful
and facile CuAAC click reaction14 of 2 with azidomethylferro-
cene and dendritic azides yielding cationic bi- and polymetallic
complexes of hexahapto-coordinated 1,2,3-triazolylmesitylene.
The redox chemistry of these new cationic bimetallic and
dendritic complexes is also detailed here.
−
superoxide O2 giving the 18-electron cyclohexadienylidene-
methylene complex [FeII(η5-Cp)(η5-C6Me5CH2)].18 It seems
that the 19-electron species triazolyl-[FeI(η5-Cp)(η6-
C6H2Me3‑)] generated at the cathode by single-electron
reduction of 5 reacts analogously with O2 from air giving
triazolyl-[FeII(η5-Cp)(η5-C6H2Me2CH2-)], although this cyclo-
hexadienylidene-methylene species has not been isolated in this
case. This reaction appears here to be faster than the
electrochemical time scale as expected; thus, it probably is
this oxidized species that is then oxidized at −0.68 V (Figure
1).
RESULTS AND DISCUSSION
■
Click Reaction of Ethynylmesitylene Complex 3 with
Azidomethylferrocene. The ethynyl derivative 3 of the
complex [FeCp(η6-C6H3Me3)]PF6, 1, is synthesized according
to the nucleophilic addition of lithium acetylideethylenedi-
amine followed by hydride abstraction by [Ph3C][PF6]
(Scheme 2). (Azidomethyl)ferrocene 4 is then used in the
CuAAC reaction with compound 3 to selectively produce 1,4-
disubstituted triazolyl (trz) complex 5 in quantitative yield
(Scheme 3).
The new dark-orange complex 5 is soluble in dichloro-
methane, THF, and chloroform and must be kept in the dark in
the solid state in order to avoid its visible-light-induced
photodecomplexation. The infrared spectroscopy shows the
disappearance of the azido group at 2097 cm−1 and the
−
appearance of the characteristic band of the PF6 anion at 839
1
cm−1. The formation of the trz group is clearly shown in H
NMR spectroscopy by the appearance of the CH2-trz and trz
CH peaks at 5.55 and 8.41 ppm, respectively, and is also
confirmed by the presence of the characteristic peaks of Cq and
CH of trz in the 13C NMR spectrum. Product 5 was
additionally characterized by HMBC, HSQC, COSY, 31P, and
19F NMR spectroscopic techniques (Supporting Information).
Finally, the structure of 5 was confirmed by the molecular peak
at 506 Da in the mass spectrum corresponding to the positively
charged complex 5 and by elemental analysis.
The cyclic voltammetry and redox chemistry of the iron-
sandwich complexes including that of ferrocene15 and of the
family of [FeCp(η6-arene)][PF6] complexes16 are well
documented. The cyclic voltammograms (CVs) of complex 5
were recorded in DMF using decamethylferrocene as the
internal reference17 in order to investigate the redox properties
of the triazolyl-[FeIICp(η6-C6H2Me3-)]PF6 group. The oxida-
tion wave at 0.55 V vs [FeCp*2]+/0 (Cp* = η5-C5Me5) is due to
Figure 1. CVs of 5 under N2 and under O2 (air). Solvent, DMF;
reference electrode, Ag; working and counter electrodes, Pt; scan rate,
0.2 V/s; and supporting electrolyte, [n-Bu4N][PF6], 0.1M.
Scheme 3. “Click” Synthesis of Bimetallic Complex 5
B
dx.doi.org/10.1021/om500495r | Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
Scheme 4. Reduction of the Complex Fc-CH2-trz-FeII(η5-Cp)(η6-C6H2Me3-)]PF6, 5, (Fc = ferrocenyl) by NaBH4 Giving Neutral
Bimetallic Complex 6 and Isomers
Figure 2. (a) FD-MS of neutral compound 6 and isomers and (b) possible hydride addition on four positions i, ii, iii, and iv of the mesitylene ligand
(ii and iv are steroelectronically disfavored).
Reduction of Binuclear Triazole Complex 5 by NaBH4.
The complexes of the [FeCp(η6-arene)][PF6] family are known
to be reducible by NaBH4 on the arene ligand producing a
decrease of hapticity to yield cyclohexadienyl complexes, and in
the presence of methyl substituents on the arene ligand, the
unsubstituted carbon atoms of the ligand are preferentially
attacked.19 In accord with this rule,20 reduction of the dark-
orange cationic complex 5 by NaBH4 at 0 °C in THF produces
the light-orange complex 6 that contains two iron-sandwich
units with both pentahapto ligands. Complex 6 is soluble in less
polar solvents such as diethyl ether, which allows its extraction
under N2 (Scheme 4). Compound 6 is air-sensitive but not
light-sensitive, contrary to the complexes of the [FeII(η5-
Cp)(η6-arene)]PF6 family.8b,21
Compound 6 together with isomers have been isolated in
80% yield, and their structure is confirmed by the observation
of the molecular peak in the FD-mass spectrum (Figure 2a).
Compound and isomers 6 have been further characterized by
1H NMR, 13C NMR, and HSQC spectroscopy, which is rather
complex, showing the formation of a mixture of isomers
corresponding to different positions of the hydride addition.
The same phenomenon has been observed for the reduction of
triazolyl-cobalticenium complexes by NaBH4.22 Indeed the
hydride reduction of compound 5 might occur on positions i, ii,
iii, and iv of the mesitylene ligand (preferentially in i and iii due
to sterically and electronically disfavored hydride attack on the
methyl-substituted arene carbon atoms) as indicated in Figure
2b. In all cases, the hydride is located in exo position on the
mesitylene ligand as a result of the exo hydride attack. No
attempt was made to identify and separate the isomers.
The cyclic voltammogram in THF shows a totally irreversible
oxidation wave at 0.20 V vs. [FeCp2*]+/0. It is suggested that
this wave corresponds to the oxidation of the compound 6 and
its isomers (Supporting Information). This wave is very large,
representing the subsequent irreversible oxidation of 6 and its
isomers back to the starting material, complex 5.
Grafting [FeCp(η6-ethynylmesitylene)][PF6] onto Den-
drimers by Click Chemistry. Grafting [FeCp(η6-
ethynylmesitylene)][PF6] on macromolecules was a challenge
because of several factors. First, the visible-light sensitivity of
the complexes of the [FeCp(η6-arene)][PF6] family and more
particularly of the click reaction products because of the
electron-withdrawing trz substituent21 leads to a rapid
decoordination of the mesitylene ligand. Then, an additional
difficulty is the solubility problem that reduces the choice of
solvent, while coordinating solvents are not permitted because
of ligand displacement due to the cationic electron-poor arene
ligand bond in 3. Finally, the steric effect of the ortho-methyl
groups that had most probably been responsible for the lack of
success of the extension of the useful hydroamination to
dendritic amines might also cause failure of the click reaction.
Finally, however, click chemistry has proved to be an efficient
way for the incorporation of 3 into dendrimers, and the
CuAAC reaction has been successfully conducted between 3
and polyazido-terminated dendritic precursors for the synthesis
of the cationic metallodendrimers.
The synthesis of the polyazido dendrimers begins with the
synthesis of arene-centered dendrimers according to the classic
CpFe+-induced nona-allylation of mesitylene in [FeCp(η6-
1,3,5-C6H3(CH3)3)][PF6]23 according to the 1 → 3 con-
C
dx.doi.org/10.1021/om500495r | Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
Scheme 5. Synthesis of the Dendrimer G0-Nona-[FeII(η5-Cp)(η6-C6H2Me3-)]PF6, 9
nectivity pioneered by Newkome.24 This reaction provides the
nonaallyl core and is followed by hydrosilylation with
chloromethyldimethylsilane25 and substitution of the terminal
chloro group in 7 by reaction with sodium azide giving the
zeroth-generation dendritic nonaazide 8. The following
dendrimer generation containing 27 terminal allyl groups is
obtained by Williamson reaction of the nona-chloro core 7 with
a phenol triallyl dendron23 according to a known procedure.23b
It is followed by substitution of the terminal chloride by the
azido group by reaction with NaN3. This sequence of reactions
provides the known first-generation dendrimer 10 containing
27 N3 termini.26
Click reactions follow between these dendritic azido
precursors and alkyne 3. The solvents in each reaction are
chosen in order to achieve the solubility of the final product
because the polycationic poly-[FeIICp(η6-C6H2Me3-)]PF6
dendrimers are soluble only in high polarity solvents. For the
synthesis of the dendrimer, G0-nona-[FeIICp(η6-C6H2Me3‑)]-
PF6, 9, DMF/H2O 4:1 is chosen as solvent, whereas for the
dendrimer of higher generation G1-27-[FeII(η5-Cp)(η6-
C6H2Me3-)]PF6, 11, a mixture of DMF/THF/H2O is used
because the azido-terminated precursor 10 is insoluble in DMF.
The temperature of the reactions is maintained at 60 °C, and
the reaction mixtures are left stirring during 16 h. The copper
salt is finally removed as [Cu(NH3)2(H2O)2] [SO4] by adding
an aqueous solution of NH3 that is left stirring with the mixture
for 15 min. The resulting dendrimers 9 (Scheme 5) and 11
(Scheme 6) are purified, after workup in the dark, by
precipitation in diethyl ether as yellowish powders. Washing
with the less polar THF solvent in which they are insoluble
permits one to separate the excess of starting material 3 and
further impurities to finally give products 9 and 11 that are fully
characterized by H, 13C, 19F,
P, HMBC, HSQC, COSY
1
31
NMR, IR, cyclic voltammetry, and elemental analysis. MALDI-
TOF analysis is also attempted for the smaller dendrimer 9 for
which the molecular peak is observed even though the mass
spectrum is an ensemble of multiple fragments due to the high
instability of the dendrimer under these conditions (see
Supporting Information).
Indeed, dendrimers 9 and 11 are very polar because the
fragment trz-[FeII(η5-Cp)(η6-C6H2Me3-)]PF6 is very hydro-
philic and soluble only in very polar solvents. Particularly,
dendrimers 9 and 11 can be dissolved in acetone, acetonitrile,
methanol, and DMF. However, these dendrimers are not
soluble in water despite the presence of several cationic
organometallic fragments at their periphery. Another observa-
tion is that dendrimers 9 and 11 are not stable in acetonitrile
solution because acetonitrile is a competing ligand with
mesitylene for coordination to iron(II), and precipitation
occurs after several hours. Furthermore, exposure of these
dendrimers to ambient light in solution or in the solid state also
leads to rapid decomplexation of the mesitylene ligand. When
kept in the dark, however, dendrimers 9 and 11 are stable
compounds.
Infrared spectroscopy is a very useful tool to monitor the
click reactions with dendrimers because the characteristic peak
of the azido groups at about 2094 cm−1 disappears at the end of
the reactions confirming their replacement by the 1,2,3-triazole
groups. The characteristic absorption of the PF6− anion of these
PF6 salts shows a strong band in the range 836−842 cm−1.
−
The absorptions due to the C−H stretching of the triazole
and Cp groups of the trz-[FeII(η5-Cp)(η6-C6H2Me3-)]PF6 unit
are found in the range 3095−3127 cm−1.
D
dx.doi.org/10.1021/om500495r | Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
Scheme 6. Synthesis of G1-27-[FeII(η5-Cp)(η6-C6H2Me3-)]PF6 Dendrimer 11
NMR spectroscopy confirms the structure of the trz-[FeII(η5-
(HSQC, HMBC, and COSY) show the correct correlation
between proton/proton and proton/carbon peaks. Finally,
elemental analysis confirms the structure of the dendrimers 9
and 11.
1
Cp)(η6-C6H2Me3-)]PF6 products. Particularly, in H NMR the
formation of the trz ring is clearly shown by the appearance of
the peaks around 8.27 ppm (in CD3OD or CD3COCD3) for
the products 9 and 11. In both cases, the peak of SiCH2-N3 at
2.7−2.8 ppm disappears, whereas the appearance of the new
peak of SiCH2-trz takes place at about 4.2 ppm. The presence
of the trz group is also confirmed by the appearance of the
characteristic peaks of Cq and CH of trz as well as SiCH2-trz in
the 13C NMR spectra. Finally, the assignments of the number
Cyclic Voltammetry of the Cationic Metalloden-
drimers 9 and 11. Both dendrimers 9 and 11 are also
studied by cyclic voltammetry using decamethylferrocene as the
internal reference,17 in DMF, a good solubility being accessible
with this solvent. Different conditions such as temperature and
air (O2)/N2 atmosphere are examined. A cathodic CV wave in
all the products is observed around −1.34 V vs [FeCp*2]0/+
and corresponds to the reduction of [FeIICp(η6-C6H2Me3‑)]-
PF6 to the 19-electron species [FeICp(η6-C6H2Me3-)]. In all
cases, this wave is single in DMF, which is explained by the
1
of protons in H NMR show the expected ratio between the
dendritic frame part and the trz-[FeII(η5-Cp)(η6-C6H2Me3‑)]-
PF6 groups. The 19F and 31P NMR spectra show the
−
characteristic peaks of the PF6 counteranion. 2-D NMR data
E
dx.doi.org/10.1021/om500495r | Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
Figure 3. CV of dendrimer 11 in DMF under N2. Internal reference, FeCp*2; reference electrode, Ag; working and counter electrodes, Pt; scan rate,
0.2 V/s; supporting electrolyte, [n-Bu4N][PF6].
weakness of the electrostatic factor between the redox sites of
the metallodendrimers, these redox centers being far from one
another and separated by long tethers.27 However, the envelope
of the redox wave is broad, which is presumably due to
electrostatic interactions differentiating the various single
electron-transfer steps.
EXPERIMENTAL SECTION
■
General Data. Reagent-grade tetrahydrofuran (THF) was predried
over Na foil and distilled from sodium-benzophenone anion under
argon immediately prior to use. All other solvents and chemicals were
used as received. The 1H NMR spectra were recorded at 25 °C with a
Bruker AVANCE II 400 MHz spectrometer. The 13C NMR spectra
were obtained in the pulsed FT mode at 100 MHz with a Bruker
AVANCE 400 spectrometer. 19F NMR spectra were recorded at 25 °C
in a 376 MHz with a Bruker AVANCE II 400 MHz spectrometer. 31P
NMR was recorded at 25 °C at 162 MHz with a Bruker AVANCE II
400 MHz spectrometer. All chemical shifts are reported in parts per
million (δ, ppm) with reference to Me4Si (TMS). The infrared (IR)
spectra were recorded on an ATI Mattson Genesis series FT-IR
spectrophotometer. The results of elemental analysis were obtained by
a Thermo Flash 2000 EA. The sample was introduced in a tin
container for NCHS analysis and in a silver container for oxygen
analysis. The mass spectra were performed by the CESAMO
(Bordeaux, France) on a QStar Elite mass spectrometer (Applied
Biosystems). The instrument is equipped with an ESI source, and
spectra were recorded in the positive mode. The electrospray needle
was maintained at 5000 V and operated at room temperature. Samples
were introduced by injection through a 20 μL sample loop into a 4500
μL/min flow of methanol from the LC pump. The mass spectrum of
compound 6 was obtained by the CESAMO on a AccuTOF-GcV
(JEOL), which is a GC-TOF. The instrument is equipped with a
sample introduction system named FD (Field Desorption). The
MALDI-TOF mass spectra were obtained by the CESAMO
(Bordeaux, France) on a PerSeptive Biosystems Voyager Elite
(Framingham, MA) time-of-flight mass spectrometer. All electro-
chemical measurements (CV) were recorded under the following
conditions: solvent, dry DMF; temperature, 20 °C; supporting
electrolyte, [nBu4N][PF6] 0.1M; working and counter electrodes, Pt;
reference electrode, Ag; internal reference, FeCp*2; scan rate, 0.200 V·
s−1.
When recording the CVs of dendrimers 9 and 11 under
aerobic (O2) atmosphere, the same phenomenon as that for
compound 5 is observed. The reduction wave of the fragments
[FeIICp(η6-C6H2Me3-)]PF6 is irreversible due to the fast
reaction of the 19-electron species with O2 (vide supra).
However, when the electrochemical experiments are performed
under nitrogen at room temperature, the cathodic wave (FeII/I
)
becomes chemically and electrochemically reversible. The peak-
to-peak potential difference between the cathodic and anodic
waves is 30−40 mV, significantly narrower compared with the
Nernstian one-electron process, probably due to some
adsorption onto the electrode. The electrochemical reversibility
involving equally all of the redox groups is due to very fast
rotation within the electrochemical time scale because all of the
redox groups come close to the electrode, provoking fast
electron transfer between these groups and the electrode,28
and/or the electron-hopping mechanism.29 The CV wave
under N2 of dendrimer 11 containing 27 [FeII(η5-Cp)(η6-
C6H2Me3-)]PF6 termini is shown in Figure 3.
CONCLUDING REMARKS
■
The currently used click reaction, i.e., the Huisgen-type
CuAAC, proves to be most useful to graft organometallic
complexes onto the periphery of dendrimers.30 Here, the newly
functionalized, easily available complex 3 is a remarkable
illustration insofar as the hydroamination of 3 could not
provide such iron-sandwich terminated dendrimers. In spite of
their sensivity to visible light and coordinating solvents such as
acetonitrile, the polycationic metallodendrimers were fully
characterized. The electron-withdrawing 1,2,3-triazolyl linkage
formed by the CuAAC reaction does not significantly perturb
the chemical and electrochemical reversibility of the cathodic
reduction to the FeI 19-electron species at least during the
electrochemical time scale under an inert atmosphere. This
chemistry adds to the versatility of the functionalization and
redox properties of the family of [FeCp(η6-arene)][PF6]
complexes that parallels the cobalticenium family and opens
the route to new cationic metallodendrimers and metal-
containing macromolecules and polyelectrolytes.
Complex 5. A mixture of 1 equiv of azidomethylferrocene (60 mg,
0.23 mmol) and 1 equiv of ethynyl compound 3 (94 mg, 0.23 mmol)
were dissolved in 3/2 distilled THF/H2O. At 0 °C, CuSO4 was added
(1 equiv; 1 M aqueous solution), followed by dropwise addition of a
freshly prepared solution of sodium ascorbate (2 equiv; 1 M aqueous
solution). The solution was allowed to stir for 12 h at r.t. under N2.
Then, an aqueous solution of ammonia was added, and the mixture
was allowed to stir for 10 min. The organic phase was washed twice
with water, dried with sodium sulfate, and filtered through paper, and
the solvent was removed in vacuo. Complex 5 was purified by
precipitation with diethyl ether and obtained as dark-orange powder in
1
quantitative yield (154 mg). H NMR of 5 (CD3COCD3, 400 MHz),
δppm: 8.41 (1H, CH of trz), 6.43 (2H, CH of mesitylene), 5.55 (2H of
trz−CH2), 5.17 (5H, CH of Cp of [FeIICp(η6-C6H2Me3-)]PF6, 4.45
(2H, CH of Cp sub. of FeCp2), 4.25 (2H, CH of Cp sub. and 5H, CH
of Cp free of FeCp2), 2.56 (3H, −CHCCH3) and 2.35 (6H,
trzCCCH3). 13C NMR of 5 (CD3COCD3, 100 MHz), δppm: 139.88
(Cq of trz), 125.86 (CH of trz), 102.80 (trz-Cq), 102.75 (trz-CCq),
F
dx.doi.org/10.1021/om500495r | Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
94.44 (CHCq of mesitylene), 88.48 (CH of mesitylene), 82.50 (Cq of
Cp sub. of FeCp2), 78.78 (CH of Cp of -[FeIICp(η6-C6H2Me3-)]PF6,
69.01 (CH of Cp of FeCp2), 68.93 and 68.88 (CH of Cp sub. of
FeCp2), 50.08 (trz-CH2), 19.61 and 19.54 (−CH3 of mesitylene). 19F
NMR of 5 (CD3COCD3, 376 MHz), δppm: doublet centered at −73.3
solution of sodium ascorbate (2.2 equiv per branch). The color of the
solution changed from yellow to dark orange upon addition of sodium
ascorbate. The reaction mixture was allowed to stir for 16 h at 60 °C
under nitrogen atmosphere. Then, the mixture of solvents was
evaporated in vacuo, and 100 mL of nitromethane was added followed
by the addition of an aqueous solution of ammonia. The mixture was
allowed to stir for 15 min in order to remove all the copper salt
trapped inside the dendrimer. The organic phase was washed twice
with water, dried over sodium sulfate, and filtered, and the solvent was
removed in vacuo. Then, the product was precipitated from an acetone
solution in diethyl ether and washed with THF to remove the excess of
alkyne and further impurities. Product 11 was obtained as an orange-
yelow powder. Yield: 56% (35 mg). 1H NMR of 11 (CD3COCD3, 400
MHz), δppm: 8.32 (27H, CH of trz), 7.30, 6.90 (39H, CH of
arom.core), 6.42 (54H, CH of mesitylene), 5.12 (135H, CH of Cp of
[FeIICp(η6-C6H2Me3-)]PF6, 4.20 (54H, SiCH2-trz), 3.59 (18H,
SiCH2O), 2.51 (3H, −CHCCH3) and 2.31 (6H, trzCCCH3), 1.73
(72H, CH2CH2CH2Si), 1.28 (72H, CH2CH2CH2Si), 0.71 (72H,
CH2CH2CH2Si), 0.10 (216H, Si(CH3)2). 13C NMR of 11
(CD3COCD3, 100 MHz), δppm: 159.58 (arom. OCq), 139.66 (Cq of
trz), 137.47 (Cq of arom.core), 127.51 and 113.81 (arom. CH), 125.59
(CH of trz), 102.76 (trz-Cq), 102.67 (trz-CCq), 94.58 (CHCq of
mesitylene), 88.53 (CH of mesitylene), 78.78 (CH of Cp of
[FeI I Cp(η6 -C6 H2 Me3 -)]PF6 , 60.20 (CH2 OAr), 43.25
(CqCH2CH2CH2Si), 42.21 (CqCH2CH2CH2Si), 40.97 (trz-CH2Si),
19.61 (−CH3 of mesitylene), 17.70 (CqCH2CH2CH2Si), 14.82
(CqCH2CH2CH2Si), −4.16 (Si(CH3)2). 19F NMR of 11
(CD3COCD3, 376 MHz), δppm: doublet centered at 73.3 ppm (JF-P
ppm (JF-P = 710 Hz). 31P NMR of 5 (CD3COCD3, 162 MHz), δppm
:
−
−144.1 ppm (hept., PF6 ) (JP-F = 710 Hz). ESI MS of 5 (m/z): Calcd
+
for C27H28N3Fe2 , 506.097 Da; found, 506.098 Da. Anal. Calcd for
C27H28N3Fe2PF6: C, 49.80; H, 4.33. Found C, 50.10; H, 4.51.
Complex 6. A mixture of 1 equiv of 5 (30 mg, 0.046 mmol) with 2
equiv of NaBH4 (1.7 mg, 0.092 mmol) in 20 mL of distilled THF was
stirred for 10 min under N2. Then, the solvent was evaporated in
vacuo, and distilled diethyl ether was added to solubilize the neutral
product. After filtration under N2 and evaporation of the solvent in
vacuo, the product was obtained as a light-orange powder. Yield: 80%
1
(19 mg). Complex 6 is not stable in air and was stored under N2. H
NMR of 6 (CDCl3, 400 MHz), δppm: 7.88−7.11 (1H, CH of trz),
6.36−6.06 (CH of mesitylene), 5.42−5.25 (2H of trz−CH2 and H of
diene), 4.93−4.00 (5H, CH of Cp of [FeIICp(η6-C6H2Me3-)]PF6 and
(9H, CH of Cp of FeCp2), 2.46−2.20 and 1.40−1.17 (9H, −CH3),
1.90−1.64 (H in exo position). 13C NMR of 6 (CDCl3, 100 MHz),
δppm: 137.65 (Cq of trz), 123.20 (CH of trz), 102.31 (trz-Cq), 98.71
(trz-CCq), 94.60 (CHCq of mesitylene), 88.33 (CH of mesitylene),
79.56 (Cq of Cp sub. of FeCp2), 79.56−75.04 (CH of Cp of
-[FeIICp(η6-C6H2Me3-)]PF6, 69.48−68.78 (CH of FeCp2), 49.93 (trz-
CH2), 39.74, 39.00 and 30,02 (CH exo), 25.65−19.96 (−CH3 of
mesitylene). MS (m/z) of 6: Calcd for C27H29Fe2N3, 507.1060; found,
507.1055.
= 710 Hz). 31P NMR of 11 (CD3COCD3, 162 MHz), δppm: −144.1
Compound 9. Azido-terminated dendrimer 8 (1 equiv, 30 mg,
0.020 mmol) and complex 3 (13.5 equiv., 110.7 mg, 0.27 mmol) were
dissolved in 20 mL of anhydrous and degassed DMF, then 3 mL of
degassed water was added, and the reaction mixture was cooled to 0
°C. Then, an aqueous solution of 1 M CuSO4 (1.1 equiv per branch)
was added dropwise, followed by the dropwise addition of a freshly
prepared solution of sodium ascorbate (2.2 equiv per branch). The
color of the solution changed from yellow to dark orange upon
addition of sodium ascorbate. The reaction mixture was allowed to stir
for 16 h at 60 °C under nitrogen atmosphere. Then, the mixture of
solvents was evaporated in vacuo, and 100 mL of nitromethane was
added followed by the addition of an aqueous solution of ammonia.
The mixture was allowed to stir for 15 min in order to remove all of
the copper salt trapped inside the dendrimer. The organic phase was
washed twice with water, dried over sodium sulfate, and filtered, and
the solvent was removed in vacuo. Then, the product was precipitated
from an acetone solution in diethyl ether and washed with THF to
remove the excess of alkyne and further impurities. Product 9 was
−
ppm (hept., PF6
) (JP-F = 710 Hz). Anal. Calcd for
C720H975Si36N81Fe27O9(PF6)27(H2O)2: C 49.76, H 5.68; found, C
49.48 H 5.81.
ASSOCIATED CONTENT
* Supporting Information
■
S
Spectroscopic data for the bimetallic and metallodendritic
complexes (IR, NMR, and mass spectra) and cyclic voltammo-
grams. This material is available free of charge via the Internet
at http://pubs.acs.org.
AUTHOR INFORMATION
Corresponding Author
*E-mail: d.astruc@ism.u-bordeaux1.fr.
■
Notes
1
obtained as an orange-yellow powder. Yield: 65% (67 mg). H NMR
The authors declare no competing financial interest.
of 9 (CD3OD, 400 MHz): δppm: 8.23 (9H, CH of trz), 7.18 (3H, CH
of arom.core), 6.33 (18H, CH of mesitylene), 5.03 (45H, CH of Cp of
[FeIICp(η6-C6H2Me3-)]PF6, 4.16 (18H, SiCH2-trz), 2.48 (27H,
−CHCCH3), 2.25 (54H, trzCCCH3) 1.80 (18H, CH2CH2CH2Si),
1.31 (18H, CH2CH2CH2Si), 0.76 (18H, CH2CH2CH2Si), 0.13 (54H,
Si(CH3)2). 13C NMR of 9 (CD3OD, 100 MHz), δppm: 145.09 (Cq of
arom.core), 138.24 (Cq of trz), 127.12 (CH of trz), 124.41 (CH of
arom.core), 102.46 (trz-Cq and trz-CCq), 94.05 (CHCq of
mesitylene), 88.34 (CH of mesitylene), 78.37 (CH of Cp of
[FeIICp(η6-C6H2Me3-)]PF6, 44.00 (CqCH2CH2CH2Si), 42.01
(CqCH2CH2CH2Si), 40.72 (trz-CH2Si), 20.34 and 20.20 (−CH3 of
mesitylene), 17.91 (CqCH2CH2CH2Si), 14.92 (CqCH2CH2CH2Si),
−4.61 (Si(CH3)2). 19F NMR of 9 (CD3OD, 376 MHz), δppm: doublet
centered at 75.3 ppm (JF-P = 710 Hz). Anal. Calcd for
C207H282Si9N27Fe9P9F54(H2O): C 47.57, H 5.48; found, C 47.64 H
5.22.
Compound 11. Azido-terminated dendrimer 10 (1 equiv, 22.5 mg,
0.004 mmol) and complex 3 (40.0 equiv, 60 mg, 0.144 mmol) were
dissolved in a mixture of 20 mL of anhydrous and degassed DMF and
15 mL of anhydrous and degassed THF, then 3 mL of degassed water
was added, and the reaction mixture was cooled to 0 °C. Then, an
aqueous solution of 1 M CuSO4 (1.1 equiv per branch) was added
dropwise, followed by the dropwise addition of a freshly prepared
ACKNOWLEDGMENTS
Helpful assistance and discussions with Claire Mouche (mass
spectrometry, CESAMO), Noel Pinaud (NMR, CESAMO),
and Jaime Ruiz (dendrimers, ISM) at the University of
Bordeaux and financial support from L’Oreal, the University
́
of Bordeaux, and the Centre National de la Recherche
Scientifique (CNRS) are gratefully acknowledged.
■
̈
REFERENCES
■
(1) (a) Newkome, G. R.; Moorefield, C. N. Chem. Rev. 1999, 99,
1689−1746. (b) Newkome, G. R.; Moorefield, C. N.; Vogtle, F.
̈
Dendrimers and Dendrons, Syntheses, Concepts, Applications; Wiley-
VCH: Weinheim, Germany, 2001. (c) Hwang, S. H.; Shreiner, C. D.;
Moorefield, C. N.; Newkome, G. R. New J. Chem. 2007, 31, 1192−
1217. (d) Vogtle, F.; Richardt, G.; Werner, N. Dendrimer Chemistry
̈
Concepts, Syntheses, Properties, Applications; Wiley: Weinheim,
Germany, 2009. (e) Astruc, D.; Boisselier, E.; Ornelas, C. Chem.
Rev. 2010, 110, 1857−1959. (f) Caminade, A.-M.; Turin, C.-O.;
Laurent, R.; Ouali, A.; Delavaux-Nicot, B. Dendrimers. Towards
Catalytic, Material and Biomedical Uses; Wiley: Weinheim, Germany,
G
dx.doi.org/10.1021/om500495r | Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
2011. (g) Campana, S.; Ceroni, P.; Punteriero, F. Designing
Dendrimers; Wiley: Hoboken, NJ, 2012.
(11) (a) Wang, Y.; Latouche, C.; Rapakousiou, A.; Lopez, C.;
Ledoux-Rak, I.; Ruiz, J.; Saillard, J.-Y.; Astruc, D. Chem.Eur. J. 2014,
20, 8076−8088.
(12) Wildschek, M.; Rieker, C.; Jaitner, P.; Schottenberger, H.;
Schwarzhans, K. E. J. Organomet. Chem. 1990, 396, 355−361.
(13) Wang, Y.; Rapakousiou, A.; Ruiz, J.; Astruc, D. Chem.Eur. J.
2014, DOI: 10.1002/chem.201403085.
(2) (a) Knapen, J. W. J.; van Dermade, A. X.; Dewilde, J. C.; van
Leuwen, P. W. N. M.; Wijkens, P.; Grove, D. M.; van Koten, G. Nature
1994, 659−663. (b) Oosterom, G. E.; Reek, J. N. H.; Kamer, P. C. J.;
van Leeuwen, P. W. N. M. Angew. Chem., Int. Ed. 2001, 40, 1828−
1849. (c) Astruc, D.; Chardac, F. Chem. Rev. 2001, 101, 2991−3024.
(d) van Heerbeeck, R.; Kamer, P. C. J.; van Leeuwen, P. W. N. M.;
Reek, J. N. H. Chem. Rev. 2002, 102, 3717−3756. (e) Astruc, D.;
(14) (a) Rostovtsev, V. V.; Green, L. G.; Fokin, V. V.; Sharpless, K. B.
Angew. Chem., Int. Ed. 2002, 41, 2596−2599. (b) Tornøe, C. W..
(b1) Christensen, C.; Meldal, M. J. Org. Chem. 2002, 67, 3057−3064.
(15) (a) Flanagan, J. B.; Margel, S.; Bard, A. J.; Anson, F. C. J. Am.
Chem. Soc. 1978, 100, 4248−4253. (b) Connelly, N. G.; Geiger, W. E.
Chem. Rev. 1996, 96, 877−910. (c) Nishihara, H. Adv. Inorg. Chem.
2002, 53, 41−86. (d) Zatsepin, T. S.; Andreev, S. Y.; Hianik, T.;
Oretskaya, T. S. Russ. Chem. Rev. 2003, 72, 537−554. (e) Zanello, P.
Inorganic Electrochemistry. Theory, Practice and Applications; RSC:
Cambridge, U.K., 2003. (f) Geiger, W. E. Organometallics 2007, 26,
5738−5765.
Heuze, K.; Gatard, S.; Mer
329−338. (f) Liang, C.; Frec
́
y, D.; Nlate, S. Adv. Synth. Catal. 2005, 347,
het, J. M. J. Prog. Polym. Sci. 2005, 30,
́
385−402. (g) Scott, R.W. J.; Wilson, O. M.; Crooks, R. M. J.
Phys.Chem. B 2005, 109, 692−704. (h) de Jesus, E.; Flores, J. C. Ind.
Eng. Chem. Res. 2008, 47, 7968−7981. (i) Wang, D.; Astruc, D. Coord.
Chem. Rev. 2013, 257, 2317−2334.
(3) (a) Percec, V.; Johansson, G.; Ungar, G.; Zhou, J. P. J. Am. Chem.
Soc. 1996, 118, 9855−9866. (b) Zeng, F.; Zimmermann, S. C. Chem.
Rev. 1997, 97, 1681−1712. (c) Balzani, V.; Campana, S.; Denti, G.;
Juris, A.; Serroni, S.; Venturi, M. Acc. Chem. Res. 1998, 31, 26−34.
(d) Matthews, O. A.; Shipway, A. N.; Stoddart, J. F. Prog. Polym. Sci.
1998, 23, 1−56. (e) Bosman, A. W.; Janssen, H. M.; Meijer, E. W.
Chem. Rev. 1999, 99, 1665. (f) Armada, M. P. G.; Losada, J.; Zamora,
M.; Alonso, B.; Cuadrado, I.; Casado, C. M. Bioelectrochemistry 2006,
(16) (a) Dessy, R. E.; Stary, F. E.; King, R. B.; Waldrop, M. J. Am.
Chem. Soc. 1966, 88, 471. (b) Moinet, C.; Roman, E.; Astruc, D. J.
́
Electroanal. Chem. 1981, 121, 241−253. (c) Lacoste, M.; Varret, F.;
Toupet, L.; Astruc, D. J. Am. Chem. Soc. 1987, 109, 6504−6506.
(d) Desbois, M.-H.; Astruc, D.; Guillin, J.; Varret, F.; Trautwein, A. X.;
Villeneuve, G. J. Am. Chem. Soc. 1989, 111, 5800−5809. (e) Ruiz, J.;
Lacoste, M.; Astruc, D. J. Am. Chem. Soc. 1990, 112, 5471−5483.
69, 65−73. (g) Balzani, V.; Bergamini, G.; Ceroni, P.; Vogtle, F. Coord.
̈
Chem. Rev. 2007, 251, 525. (h) Martinez, F. J.; Gonzales, B.; Alonso,
B.; Losada, J.; Garcia-Armada, M. P.; Casado, C. M. J. Inorg.
Organomet. Polym. Mater. 2008, 18, 51−58.
(17) Ruiz, J.; Astruc, D. C. R. Acad. Sci. 1998, t. 1, Ser
(18) Astruc, D.; Hamon, J.-R.; Roman, E.; Michaud, P. J. Am. Chem.
Soc. 1981, 103, 7502−7514.
́
. IIc, 21−27.
́
(4) (a) Jiang, D.-L.; Aida, T. J. Am. Chem. Soc. 1999, 121, 10895−
10901. (b) Andronov, A.; Frechet, J. M. J. Chem. Commun. 2000,
́
(19) Khand, U.; Pauson, P. L.; Watts, W. E. J. Chem. Soc. C 1968,
2257−2259.
1701−1710. Astruc, D. Nat. Chem. 2012, 4, 255−267. Bergamini, G.;
Marchi, E.; Ceroni, P.; Balzani, V. In Designing Dendrimers; Campagna,
S., Ceroni, P., Puntoriero, F., Eds.; Wiley: Hoboken, NJ, 2012; pp
341−366.
(20) (a) Davies, S. G.; Green, M. L. H.; Mingos, D. M. P. Tetrahedron
1978, 34, 20−50. (b) Astruc, D.; Michaud, P.; Madonik, A.; Saillard, J.-
Y.; Hoffmann, R. Nouv. J. Chim. 1985, 9, 41−50.
(21) Gill, T. P.; Mann, K. R. Inorg. Chem. 1980, 19, 3007−3010.
(b) Gill, T. P.; Mann, K. R. J. Organomet. Chem. 1981, 216, 65−71.
(22) Rapakousiou, A.; Mouche, C.; Duttine, M.; Ruiz, J.; Astruc, D.
Eur. J. Inorg. Chem. 2012, 5071−5077.
(5) (a) Casado, C. M.; Moran
J. Appl. Organomet. Chem. 1999, 13, 245−259. (b) Casado, C. M.;
Cuadrado, I.; Moran, M.; Alonso, B.; Garcia, B.; Gonzales, B.; Losada,
́
, M.; Alonso, B.; Barranco, M.; Losada,
́
J. Coord. Chem. Rev. 1999, 185−186, 53. (c) Casado, C. M.; Alonso,
B.; Losada, J.; Garcia-Armada, M. P. In Designing Dendrimers;
Campagna, S., Ceroni, P., Puntoriero, F., Eds.; Wiley: Hoboken, NJ,
2012; pp 219−262.
(23) (a) Moulines, F.; Djakovitch, L.; Boese, R.; Gloaguen, B.; Thiel,
W.; Fillaut, J.-L.; Delville, M.-H.; Astruc, D. Angew. Chem., Int. Ed.
1993, 32, 1075−1077. (b) Valerio, C.; Fillaut, J. L.; Ruiz, J.; Guittard,
́
J.; Blais, J. C.; Astruc, D. J. Am. Chem. Soc. 1997, 119, 2588−2589.
(24) (a) Newkome, G. R.; Yao, Z.; Baker, G. R.; Gupta, V. K. J. Org.
Chem. 1985, 50, 2003−2004. (b) Newkome, G. R.; Shreiner, C. Chem.
Rev. 2010, 110, 6338−6442.
(25) (a) Sartor, V.; Djakovitch, L.; Fillaut, J.-L.; Moulines, F.; Neveu,
F.; Marvaud, V.; Guittard, J.; Blais, J. C.; Astruc, D. J. Am. Chem. Soc.
1999, 121, 2929−2930. (b) Ruiz, J.; Lafuentes, G.; Marcen, S.;
Ornelas, C.; Lazare, S.; Cloutet, E.; Blais, J.-C.; Astruc, D. J. Am. Chem.
Soc. 2003, 125, 7250−7257.
(26) (a) Ornelas, C.; Ruiz, J.; Belin, C.; Astruc, D. J. Am. Chem. Soc.
2009, 131, 590−601. (b) Boisselier, E.; Diallo, A. K.; Salmon, L.;
Ornelas, C.; Ruiz, J.; Astruc, D. J. Am. Chem. Soc. 2010, 132, 2729−
2742. (c) Djeda, R.; Rapakousiou, A.; Liang, L.; Guidolin, N.; Ruiz, J.;
Astruc, D. Angew. Chem., Int. Ed. 2010, 49, 8152−8156.
(27) (a) Sutton, J. E.; Sutton, P. M.; Taube, H. Inorg. Chem. 1979, 18,
1017−1024. (b) Richardson, D. E.; Taube, H. Coord. Chem. Rev. 1984,
(6) (a) Casado, C. M.; Gonzal
Moran, M.; Losada, J. Angew. Chem., Int. Ed. 2000, 39, 2135−2138.
(b) Takada, K.; Diaz, D.; Abruna, H. D.; Cuadrado, I.; Gonzales, B.;
́
ez, B.; Cuadrado, I.; Alonso, B.;
́
̃
Casado, C. M.; Alonso, B.; Moran
́
, M.; Losada, J. Chem.Eur. J. 2001,
7, 1109−1117. (c) Yao, H.; Grimes, R. N.; Corsini, M.; Zanello, P.
Organometallics 2003, 22, 4381−4383. (d) Rapakousiou, A.; Wang, Y.;
Belin, C.; Pinaud, N.; Ruiz, J.; Astruc, D. Inorg. Chem. 2013, 52, 6685−
6693.
(7) For dendrimers terminated by [Fe(η5-C5H4-)(η6-C6Me6)][PF6]
groups, see Djeda, R.; Ornelas, C.; Ruiz, J.; Astruc, D. Inorg. Chem.
2010, 49, 6085−6101.
(8) (a) Nesmeyanov, A. N. Adv. Organomet. Chem. 1972, 10, 1−16.
(b) Hamon, J.-R.; Astruc, D.; Michaud, P. J. Am. Chem. Soc. 1981, 103,
758−766. (c) Green, J. C.; Kelly, M. R.; Payne, M. P.; Seddon, E. A.;
Astruc, D.; Hamon, J.-R.; Michaud, P. Organometallics 1983, 2, 211−
218. (d) Moulines, F.; Astruc, D. Angew. Chem., Int. Ed. Engl. 1988, 27,
1347−1349. (e) Abd-El-Aziz, A. S.; Bernardin, S. Coord. Chem. Rev.
2000, 203, 219−267. (f) Abd-El-Aziz, A. S.; Todd, E. K. Coord. Chem.
Rev. 2003, 246, 3−52.
60, 107−129. (c) Barrier
̀
e, F.; Geiger, W. E. Acc. Chem. Res. 2010, 43,
1030−1039.
(28) Gorman, C. B.; Smith, B. L.; Parkhurst, H.; Sierputowska-Gracz,
H.; Haney, C. A. J. Am. Chem. Soc. 1999, 121, 9958−9966.
(29) Amatore, C.; Bouret, Y.; Maisonhaute, E.; Goldsmith, J. I.;
(9) (a) Sheats, J. E.; Rausch, M. D. J. Org. Chem. 1970, 35, 3245−
3249. (b) Geiger, W. E. J. Am. Chem. Soc. 1974, 96, 2632−2634.
(c) Sheats, E. J. Organomet. Chem. Libr. 1979, 7, 461−521. (d) Kemmit,
R. D. W.; Russel, D. R. In Comprehensive Organometallic Chemistry;
Pergamon Press: Oxford, U. K., 1982; Vol 5, Chapter 34, 4.5.1, pp
244−248. (e) Gloaguen, B.; Astruc, D. J. Am. Chem. Soc. 1990, 112,
4607−4609.
Abruna, H. D. Chem.Eur. J. 2001, 7, 2206−2226.
̃
(30) Wang, Y.; Salmon, L.; Ruiz, J.; Astruc, D. Nat. Commun. 2014,
DOI: 10.1038/ncomms4489.
(10) Astruc, D. Organometallic Chemistry and Catalysis; Springer:
Heidelberg, Germany, 2008; Chapter 10, pp 275−286.
H
dx.doi.org/10.1021/om500495r | Organometallics XXXX, XXX, XXX−XXX