1′-Trimethylsilylethynyl-, 1′-ethenyl- and 1′-formyl-1- ethynylferrocenes: Syntheses and electrochemical properties

Article abstract of DOI:10.1016/j.tet.2013.01.093

Efficient syntheses of 1′-trimethylsilylethynyl-, 1′-ethenyl-, and 1′-formyl-1-ethynylferrocenes are reported. The majority of these compounds exhibit chemically reversible ferrocene-based oxidation processes from cyclic voltammetry and thereby constitute

Full text of DOI:10.1016/j.tet.2013.01.093

Tetrahedron 69 (2013) 3316e3322
Contents lists available at SciVerse ScienceDirect
Tetrahedron
journal homepage: www.elsevier.com/locate/tet
10-Trimethylsilylethynyl-, 10-ethenyl- and 10-formyl-1-
ethynylferrocenes: syntheses and electrochemical properties
,
,
*
Guillaume Grelaud a b, Gilles Argouarch a, Marie P. Cifuentes b, Mark G. Humphrey b
,
a,
*
ꢀ ꢀ
Frederic Paul
a
ꢀ
UMR CNRS 6226, Universite de Rennes 1, 263 avenue du General Leclerc, 35042 Rennes Cedex, France
b Research School of Chemistry, Australian National University, Canberra, ACT 0200, Australia
a r t i c l e i n f o
a b s t r a c t
Efficient syntheses of 10-trimethylsilylethynyl-, 10-ethenyl-, and 10-formyl-1-ethynylferrocenes are re-
ported. The majority of these compounds exhibit chemically reversible ferrocene-based oxidation pro-
cesses from cyclic voltammetry and thereby constitute key synthons for the development of redox-
switchable molecular systems.
Article history:
Received 24 November 2012
Received in revised form 16 January 2013
Accepted 31 January 2013
Available online 13 February 2013
Ó 2013 Elsevier Ltd. All rights reserved.
Keywords:
1,10-Functional ferrocenes
Cyclic voltammetry
1. Introduction
develop redox-switchable NLO-active group 8 metalealkynyl
complexes incorporating this particular fragment and demon-
Since its discovery in the early 1950s,1 ferrocene has attracted
considerable attention in diverse areas, such as catalysis, materials
science, and bio-organometallic chemistry.2 Much of this interest
has been driven by the great structural diversity attainable from
this redox-active scaffold, with a large variety of ferrocene-
containing synthons already reported or directly available from
commercial suppliers, a feature that results from the versatility of
chemical reactions undergone by this simple molecule. An addi-
tional interest is the remarkable stability of this particular organ-
ometallic moiety in the Fe(II) and Fe(III) redox states2a compared to
other redox couples with similar synthetic flexibility. These prop-
erties have made ferrocene a very popular building block for de-
strated their grafting on hydrogenated silicon surfaces.7,8
During these investigations the difunctional 10-trialkylsilylethynyl-
1-ethynylferrocene derivative 1 was required (Scheme 1). Considering
the large scope of reactions undergone by alkynes in organic and or-
ganometallic chemistry,9 1 is a strategic building block for accessing
differently functionalized 1,10-bisalkynylferrocenes and their de-
rivatives. We now report a reliable and selective synthesis of 1 in a few
steps from the known 1-iodo-10-formylferrocene (8)10 along with
syntheses of the related synthons 1-ethynyl-10-ethenylferrocene (6)
and 1-ethynyl-10-formyl-ferrocene (7), which also afford possibilities
for grafting on hydrogenated silicon.11
veloping
redox-switchable
functional
molecules.3
More
2. Results and discussion
specifically, in the field of nonlinear optics (NLO), ferrocene was
utilized as early as the mid 1980s as an organometallic donor group
in dipolar architectures by Green, Marder, and co-workers.4 Fol-
lowing these seminal studies, a plethora of ferrocene-containing
compounds were developed and studied for their second- and
third-order NLO properties by various techniques. These were often
shown to exhibit significant NLO responses,5 which can be modu-
lated upon oxidation of the ferrocenyl unit, as experimentally
demonstrated more recently.6 In this context, we have also tried to
In spite of the fact that various syntheses have been reported for
ethynylferrocene (2),12e18 an efficient synthetic route to 1 has not
been reported to date, despite the numerous reactions available for
the introduction of alkynyl functionalities on ferrocene
moieties.16e22 Note that 1,10-diethynylferrocene (3) is not a kineti-
cally stable molecule (Scheme 1); unlike its 1,2-isomer,19 3 has
never been isolated,23 since it spontaneously polymerizes in solu-
tion unless trimethylsilyl14,15 or dimethylcarbinol14 protecting
groups are present on both alkynes (e.g., 4). Thus, attempts to se-
lectively remove one of the two trimethylsilyl groups of 4 never led
to the selective and quantitative formation of the mono-
deprotected compound 1.15,18,20,23 For example, when a source of
* Corresponding authors. E-mail addresses: mark.humphrey@anu.edu.au (M.G.
Humphrey), frederic.paul@univ-rennes1.fr (F. Paul).
0040-4020/$ e see front matter Ó 2013 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.tet.2013.01.093

G. Grelaud et al. / Tetrahedron 69 (2013) 3316e3322
3317
Scheme 1. Selected ferrocene derivatives.
potentially nucleophilic methoxide anions was used for the
deprotection, such as with methanolic KOH, the [4]-
ferrocenophane compound
which is akin to the synthesis of functional [4]-ferrocenophanes
from various 1,10-bis(alkynyl)-ferrocenes and phenol or acetic
acid, demonstrates that trans-annular addition is a reaction easily
undergone by 1,10-bisalkynyl derivatives in the presence of various
nucleophiles.24
halide in Sonogashira couplings.22 In the second step, the formyl
group in 9 was converted into a terminal alkyne by first reacting 9
with CBr4/PPh3/Zn in CH2Cl2 to afford the dibromo-alkene 10 in 92%
yield, and then treating 10 with excess LDA in THF at low tempera-
ture, followed by quenching with aqueous NH4Cl. By this route,1 was
obtained in 72% overall yield from 8 as an isolable compound
(Scheme 2).
In spite of a slow decomposition taking place over prolonged pe-
riods of time, which has thus far precluded characterization of this
compound by elemental analysis, 1, when employed immediately
after its synthesis, is nevertheless sufficiently stable to be further
functionalized. Thus, Sonogashira coupling with p-bromoni-
trobenzene afforded the expected cross-coupled product 11 in good
yield after chromatographic purification and recrystallization
(Scheme 3). Under the reaction conditions used, no degradation of 1
occurred, as only 11 and excess of unreacted 1 or traces of its homo-
coupling product were observed in the crude reaction mixture (TLC).
The next target, 6, was obtained from the alkenyl analogue of 1
(12), which can itself be obtained by Wittig olefination31 of 9 using
methylidenetriphenylphosphorane, generated from n-BuLi and
methyltriphenylphosphonium bromide in THF at 0 ꢀC (Scheme 4).
Alkene derivative 12 was isolated in 95% yield, 79% overall yield
from 8.
5
was formed.18,20 This reaction,
In order to limit any undesirable trans-annular addition when
attempting to synthesize 1, it was decided to introduce the terminal
alkyne at the latest possible stage in the absence of strong nucleo-
philes. This was done by mimicking the synthesis of various
(ethynylphenyl)ethynyl-trimethylsilanes from the corresponding
bromobenzaldehydes25 using
a
Sonogashira coupling26/Cor-
eyeFuchs27 reaction sequence. These reactions and related ones
have ample precedence in ferrocene chemistry.16e22,28 The protected
alkyne moiety was first introduced by palladium-catalyzed cross-
coupling of 8 with trimethyl-ethynylsilane and the expected 1-
trimethylsilylethynyl-10-formylferrocene 9 was obtained in 83%
yield. Note that with the bromo analogue of 8, 9 was not obtained,
even when the more active P(t-Bu)3/[PdCl2(PhCN)2] catalytic system
was used,29,30 and regardless of the reaction being carried out at
higher temperatures (80 ꢀC) and/or over extended reaction times (up
to 72 h). This result is consistent with previous reports of poor re-
activity of 10-bromo-1-ethynylferrocene when used as the organic
Aware of the possibility of [4]-ferrocenophane formation in
the presence of alkoxide, especially methoxide anions, the
Scheme 2. Synthesis of 1 from 8.

3318
G. Grelaud et al. / Tetrahedron 69 (2013) 3316e3322
Scheme 3. Synthesis of 11 from 1.
CH2
CH
CHO
Ph3P=CH2
Fe
Fe
THF, 0°C to RT
95 %
C C SiMe3
C C SiMe3
9
12
Scheme 4. Synthesis of 12 from 9.
deprotection of 12 was investigated under two different sets of
conditions: (i) with methanolic KOH and (ii) with fluoride ion
(TBAF) in THF. In the first case, the reaction resulted in the for-
mation of the [4]-ferrocenophane 13 in good yield and its
structure was confirmed by 2D NMR (cf. Supplementary data). In
contrast, when the weaker fluoride nucleophile was used to
desilylate 12, the desired terminal acetylene 6 was obtained
nearly quantitatively as a stable compound (Scheme 5). However,
this compound could only be isolated in at most 95% purity (by
NMR, cf. Supplementary data), as extensive decomposition on
both silica and alumina supports precluded further purification
by chromatography. Nevertheless, its fair chemical stability re-
mains quite surprising, especially considering the instability to-
ward air and/or moisture reported for the 1,10-diethenyl-32 and
1,10-diethynylferrocenes,23 and to a lesser extent for 1-ethenyl-2-
ethynylferrocene.19
totally ruled out at this stage. The coexistence of several reaction
pathways leading to 13 is also plausible. The formation of 13 is
regiospecific: no products resulting from methoxide addition at the a-
carbon atom of the ethynyl was detected in thecrude reaction mixture
by 1H NMR. This difference in reactivity between the ethenyl and the
ethynyl groupsis readilyexplained by thedifferenceinelectrophilicity
of their respective
is muchmore electrophilic duetothe lower
to that of an ethynyl group. This type of methoxide addition at the
a
-carbon atoms: that of the ethenyl group in 12/13
p
electron density relative
a-
carbon seems to be a general feature of 1-alkynylferrocenes bearing
another unsaturated substituent (alkene or alkyne) at the 10 position,
since treatment of ethenylferrocene under similar conditions does not
lead to the formation of 1-(methoxyethyl)ferrocene, ethenylferrocene
being quantitatively recovered after the aqueous work up. Similarly,
trimethylsilylethynylferrocene only gives ethynylferrocene (2) and
not the corresponding ethenyl methyl ether when reacted with KOH
in MeOH.20
A tentative mechanism can be proposed for the formation of the
[4]-ferrocenophane 13 based on the formation of
(Scheme 6).18,20 It involves desilylation of 12 followed by attack of the
methoxide anion on the -carbon atom of the ethenyl group. How-
ever, some questions remain regarding the actual step during which
desilylation takes place; the intermediacy of trimethylsilyl-
substituted alkyne undergoing the transannular addition cannot be
5
from
4
The last target, the known 1-ethynyl-10-formylferrocene (7)33
was readily obtained in either 61% or 71% yields from the formyl
precursor 9 under the deprotection conditions previously employed
for 12 (Scheme 7), affording 7 in a good overall yield of 59% in two
steps from 8. Note that 7, similar to 1, slowly decomposes when
stored over prolonged periods of time.
a
a
CH2
CH
TBAF
Fe
THF, 0°C to RT
CH2
CH
C CH
97%
6
Fe
OMe
C C SiMe3
KOH
MeOH, 0°C to RT
87%
12
Fe
13
Scheme 5. Reactivity of 12 toward TBAF in THF or methanolic KOH.

G. Grelaud et al. / Tetrahedron 69 (2013) 3316e3322
3319
CH2
CH
OMe
KOH
Fe
Fe
MeOH
C C SiMe3
13
12
H+
aqueous work up
OMe
CH
CH2
Fe
Fe
C CH
MeO-
CH
CH2
Fe
C CH
Scheme 6. Proposed mechanism for the methoxide-induced cyclization of 12.
TBAF
THF, 0°C to RT
CHO
CHO
Fe
Fe
63%
C CH
C C SiMe3
KOH
9
7
MeOH, 0°C to RT
71%
Scheme 7. Reactivity of 9 toward TBAF in THF or methanolic KOH.
Because the redox chemistry of these derivatives is often central
to their use as electro-active synthons, these compounds have been
characterized by cyclic voltammetry at a platinum electrode to
confirm that aspect (Table 1). As is often observed with ferrocene
derivatives, the values of the oxidation potential correlate with the
electronic properties of the substitutents.34,35 When 1, 12, and 9 are
compared with ethynyl (2), ethenyl, and formylferrocene, re-
spectively, the introduction of a trimethylsilylethynyl substituent
on the 10 position induces an increase in the oxidation potential
value of 110 mV (1), 70 mV (12), and 60 mV (9). The same effect is
observed for ethenylferrocene and 6 and formylferrocene and 7
(þ130 mV). These anodic shifts of the E1/2 values are readily
explained by the electron-withdrawing nature of these alkynyl
substituents relative to ferrocene,36 rendering the Fe(II) center
more difficult to oxidize.37 In the case of 11, in addition to this
metal-centered oxidation, a very cathodic and pseudo-reversible
process is found at ꢁ1.08 V, which most likely corresponds to the
reduction of the nitro group, its value being very close to that re-
ported for (p-nitrophenyl)-ethynyltrimethylsilane (ꢁ1.01 V) and
nitrobenzene (ꢁ1.19 V) under similar conditions.38 Compared to 5,
the more negative value found for 13 is consistent with the pres-
ence of only one alkenyl substituent on the annular bridge. Within
experimental uncertainty, this value is comparable to that reported
Table 1
Electrochemical data for the Fe(III)/Fe(II) oxidation in 1e2, 5e7, 9e13 and related
mono-substituted ferrocene derivativesa
b
c
Compound
E1/2
D
Ep
iPa/iPc
Ref
1
2
11
0.74
0.63
0.74
ꢁ1.08
0.46
0.47
0.53
0.59
0.77
0.83
0.68
0.90
0.48
0.55
0.47
126
128
78
110
116
d
1
1
0.9
1
This work
This work
This work
FceCH]CH2
1,10-Diethenylferrocene
12
6
FceC(O)H
9
10
7
0.9
This work
18
irrev.d
122
107
113
76
1
0.7
1
1
1
1
1
1
1
This work
This work
This work
This work
This work
This work
This work
18
72
105
106
d
13
5
1,10-(4-Hydroxy-1-
butenylene)ferrocene
d
18
a
Conditions: CH2Cl2 solvent, 0.1 M [nBu4N][PF6] supporting electrolyte, 20 ꢀC, Pt
electrode, sweep rate 0.10 V sꢁ1
.
b
E1/2 values are in V vs SCE, FcH/FcHþ as internal calibrant (0.46 V vs SCE).
Peak-to-peak separation (mV).
Chemically irreversible oxidation.
c
d

3320
G. Grelaud et al. / Tetrahedron 69 (2013) 3316e3322
for the closely related hydroxyl ferrocenophane 1,10-(4-hydroxy-
L
-
at 60 ꢀC for 36 h. After removal of solvents and volatiles under vac-
uum and following standard work up, the crude oil was adsorbed
onto silica and subjected to column chromatography (silica gel,
4.5ꢂ20 cm), eluting with hexanes/Et2O (2:1). Removal of solvents
from the combined fractions gave a red oil that was subjected to
vacuum (30 mbar, 40 ꢀC) to give 9 as a dark red solid (1.87 g, 83%). Rf
(hexanes/Et2O 2:1): 0.35. Mp: 64 ꢀC. Elemental Analysis Calcd for
C16H18FeOSi: C: 61.94; H: 5.85; found: C: 62.02, H: 5.91. HRMS (ESI):
m/z calcd for C16H18FeNaOSi [MþNa]þ: 333.0374, found: 333.0373. IR
(KBr, cmꢁ1): 2829 (m, nC(O)eH), 2148 (s, nC^C), 1691 (s, nC]O), 1245 (s,
butenylene)ferrocene.20 Except for the 1-ethynyl-10-ethenylferro-
cene 6, and perhaps the nitro derivative 11, an apparent chemical
reversibility of the metal-centered oxidation process is observed at
the electrode for all the new compounds synthesized in these
studies.39
3. Conclusions
We have described a practical and efficient synthesis of 10-tri-
methylsilylethynyl-1-ethynylferrocene (1) and of its related ethenyl
(12) and formyl (9) analogues. These compounds are quite stable
under standard laboratory conditions, as are their desilylated par-
ents 6/7 featuring a pendant ethynyl group. Further functionaliza-
tion of these derivatives by cross-coupling chemistry can easily be
effected, as demonstrated by the straightforward preparation of 11
from 1. In the field of metal alkynyl complexes, compounds such as
1 should provide simple access to a wealth of unsymmetrical 1,10-
bismetalla-alkynylferrocenyl trinuclear complexes, which have
thus far proven problematic to obtain.9d We have also shown that
KOH/MeOH or related alkoxy-containing mixtures should be avoi-
ded for cleavage of the trimethylsilyl protecting groups in com-
pounds such as 12, as this leads to the selective formation of
ferrocenophane derivatives as in the case of 4 and 1. Finally, we
have observed that, in almost all cases, the iron-centered oxidation
processes are chemically reversible at the electrode. These syn-
thons should find considerable utility in extended redox-active
assemblies and new ferrocene-based materials.41
nSieC). 1H NMR (300 MHz, CDCl3, ppm):
d 9.93 (s, 1H, CHO), 4.80, 4.60,
4.52, and 4.27 (4ꢂ t, 4ꢂ 2H, 3JH,H¼2 Hz, C5H4), 0.23 (s, 9H, SiMe3). 13
C
{1H} NMR (125 MHz, CDCl3, ppm):
d 193.6 (s, CHO), 102.0 (s,
C^CeSiMe3), 92.8 (s, C^CeSiMe3), 80.1 (s, Cquat C5H4eCHO), 75.2,
73.1, 71.2, and 70.2 (4ꢂ s, C5H4), 67.2 (s, Cquat C5H4eC^C(SiMe3)), 0.1
(s, SiMe3).
4.1.2. 10-Trimethylsilylethynyl-1-(gem-dibromoethenyl)ferrocene
(10). Carbon tetrabromide (1.66 g, 5.0 mmol) was added in small
portions to triphenylphosphine (1.31 g, 5.0 mmol) and zinc dust
(0.327 g, 5.0 mmol) in CH2Cl2 (10 mL) at 0 ꢀC. After 24 h of stirring at
room temperature, the resulting suspension was cooled to 0 ꢀC and
a solution of 10-trimethylsilylethynyl-1-formylferrocene (9; 0.62 g,
2.0 mmol) in CH2Cl2 (5 mL) was added dropwise over 5 min. The
cold bath was removed, and the reaction mixture stirred for 6 h at
room temperature and then filtered through a small pad of silica gel
(4ꢂ5 cm). The pad was washed with CH2Cl2 (150 mL) to elute all the
orange materials and the solvents were removed from the com-
bined filtrates under reduced pressure. The crude oil was purified
by column chromatography (silica gel, 4ꢂ20 cm). An orange band
was eluted with hexanes/Et2O (95:5), collected and taken to dry-
ness. The orange oil was dissolved in CH2Cl2 (5 mL) and MeOH
(10 mL), and the volume of the resultant solution was reduced to
z5 mL and then cooled to ꢁ90 ꢀC in an EtOH/N2 bath. After 30 min
at ꢁ90 ꢀC, the flask was removed from the cooling bath and the
solvents were removed from the solid mass by cannula filtration
upon warming to room temperature. Drying of the orange solid in
vacuo afforded 10 (0.86 g, 92%). Rf (hexanes/Et2O [99:1]): 0.51. El-
emental Analysis Calcd for C17H18Br2FeSi: C: 43.81, H: 3.89, found:
C: 44.05, H: 3.90. HRMS (ESI): calcd for C17H18Br2FeSi [M]þ:
463.8894, found: 463.8896. IR (KBr, cmꢁ1): 3103 and 3099 (w,
4. Experimental section
4.1. General
All air and/or moisture sensitive manipulations were performed
under an atmosphere of argon in distilled and deoxygenated sol-
vents
using
standard
Schlenk
techniques.
10-Iodo-1-
formylferrocene (8)10 and [PdCl2(PPh3)2]42 were prepared accord-
ing to the literature methods, while other chemicals were obtained
commercially and used without further purification. Standard work
up consists of extraction of the reaction mixtures/solid residues
with Et2O (with filtration if necessary), washing of the organic
extracts with water and saturated aqueous NaCl, drying over
MgSO4, filtration, and removal of the solvent under reduced pres-
sure. Flash column chromatography was performed using silica gel
(Merck Kieselgel 60, 230e400 mesh) in glass columns of various
sizes (indicated as diameterꢂlength). Unless otherwise stated Rf
values were measured on silica plates. Preparative thin-layer
chromatography was carried out on glass plates (20ꢂ20 cm)
coated with silica (Merck 60 GF254, 0.5 mm thick). 1H and 13C NMR
spectra were recorded on Bruker DPX200, Bruker Ascend 400 MHz
NMR or Bruker AVANCE 500 spectrometers, respectively, chemical
n
]CeH), 2146 (s, nC^C), 1656 (w, nC]C), 1245 (s, nSieC), 845 (s,
679 (m, dCeBr). 1H NMR (300 MHz, CDCl3, ppm):
7.16 (s, 1H, eCH]
CBr2), 4.65, 4.45, 4.34, and 4.23 (4ꢂ m, 4ꢂ 2H, C5H4), 0.24 (s, 9H,
SiMe3). 13C{1H} NMR (125 MHz, CDCl3):
134.6 (s, ]CBr2), 103.1 (s,
d]CeH),
d
d
C^C(SiMe3)), 91.8 (s, C^C(SiMe3)), 84.6 (s, eCH]), 80.9 (s, Cquat
C5H4), 73.0, 71.3, 70.8, and 70.1 (4ꢂ s, C5H4), 66.4 (s, Cquat C5H4), 0.2
(s, SiMe3).
4.1.3. 10-Trimethylsilylethynyl-1-ethynylferrocene (1). A solution of
lithium diisopropylamide, prepared from diisopropylamine
(0.76 mL, 5.40 mmol) and n-BuLi (3.10 mL of a 1.60 M solution in
hexanes, 4.95 mmol) in THF (5 mL) at 0 ꢀC, was added dropwise
over 10 min to 10-trimethylsilylethynyl-1-(gem-dibromoethenyl)
ferrocene (10; 0.70 g, 1.50 mmol) in THF (15 mL) at ꢁ90 ꢀC. After
1.5 h of stirring at ꢁ90 ꢀC, the reaction mixture was hydrolyzed
with saturated aqueous NH4Cl (10 mL), warmed to room temper-
ature and then subjected to a standard work up. The crude oil was
quickly chromatographed (silica gel, 4ꢂ15 cm) using hexanes/Et2O
(95:5) as the eluent. The orange band was collected and the solvent
evaporated under reduced pressure. The resulting orange oil crys-
tallized upon standing at ꢁ20 ꢀC for 16 h to give 1 as a low-melting
orange solid (0.43 g, 94%). Rf (hexanes/Et2O [99:1]): 0.65. Mp:
<45 ꢀC. HRMS (ESI) Calcd for C17H18FeSi [M]þ: 306.0527, found:
shifts being referenced to the residual chloroform signal
(d
7.26 ppm for 1H, 77.0 ppm for 13C). High resolution mass spectra
were obtained on a double quadrupole Waters Q-tof 2 equipped
with an orthogonal time of flight analyzer and an electrospray
source. Cyclic voltammograms were recorded using a PAR 263 in-
strument in dichloromethane solvent at 20 ꢀC (0.1 M [n-Bu4N][PF6])
with 100 mV/s scan rate at a platinum disk (1 mm diameter) using
an SCE reference electrode and ferrocene as internal calibrant
(0.46 V).43
4.1.1. 10-Trimethylsilylethynyl-1-formylferrocene (9). Trimethylsilylac-
etylene (1.55 mL, 10.88 mmol) was added to 10-iodo-1-formyl-ferro-
cene (8; 2.46 g, 7.25 mmol), [PdCl2(PPh3)2] (0.255 g, 0.36 mmol), and
CuI (0.138 g, 0.73 mmol) in THF/diisopropylamine (1:1, 50 mL) at 0 ꢀC.
The reaction mixture was warmed to room temperature and heated
306.0526. IR (KBr, cmꢁ1): 3304 (s,
(m, nC^C(H)), 1248 (s, nSieC), 652 (s,
n
^CeH), 2148 (s, nC^CðSiMe Þ), 2110
3
d
^CeH). 1H NMR (300 MHz,

G. Grelaud et al. / Tetrahedron 69 (2013) 3316e3322
3321
CDCl3, ppm):
d
4.45 (t, 3JH,H¼2 Hz, 4H, C5H4), 4.23 (dt, 3JH,H¼2 and
cooling bath was removed, the reaction mixture was stirred for 1 h
at room temperature, quenched with water (0.50 mL) and then
concentrated under reduced pressure. The orange oil (0.115 g, 97%,
approx. 95% pure by NMR) obtained after standard work up was
freed of traces of solvent by prolonged drying under moderate
vacuum (25 mbar). Extensive decomposition on both silica and
alumina prevented further purification of 6 by chromatography. Rf
(alumina, hexanes): 0.64. HRMS (ESI): Calcd for C14H13Fe [MþH]þ:
3 Hz, 4H, C5H4), 2.77 (s, 1H, ^CH), 0.24 (s, 9H, SiMe3). 13C{1H} NMR
(125 MHz, CDCl3, ppm):
d 102.8 (s, C^C(SiMe3)), 91.5 (s,
C^C(SiMe3)), 81.5 (s, C^C(H)), 74.2 (s, C^C(H)), 73.5, 73.4, 71.3,
and 71.1 (4ꢂ s, C5H4), 66.5 and 65.4 (2ꢂ s, Cquat C5H4), 0.3 (s, SiMe3).
No accurate elemental analysis of 1 could be obtained due to its
slow decomposition.
4.1.4. 10-Trimethylsilylethynyl-1-(p-nitrophenyl)ethynylferrocene
(11). 10-Trimethylsilylethynyl-1-ethynylferrocene (1; 0.336 g,
1.10 mmol), p-bromonitrobenzene (0.202 g, 1.0 mmol),
[PdCl2(PPh3)2] (0.0175 g, 0.025 mmol), and CuI (0.0095 g,
0.050 mmol) in THF/diisopropylamine (1:1, 20 mL) were heated at
40 ꢀC for 16 h. The solvents were removed, and the crude solid ob-
tained following standard work up of the residue was adsorbed onto
silica and placed on the top of a chromatographic column (silica gel,
3.5ꢂ20 cm). Elution with hexanes/CH2Cl2 (3:1) gave two bands: the
first orange band comprised homocoupled alkyne and the unreacted
starting acetylene, while the second burgundy-red band contained
the title compound. After evaporation of solvents and re-
crystallization of the residue from hexanes at ꢁ18 ꢀC, red crystals of
11 were collected on a sintered glass funnel, washed with cold
hexanes (5 mL) and dried in vacuo (0.372 g, 87%). Rf (hexanes/CH2Cl2
[3:1]): 0.37. Elemental Analysis Calcd for C23H21FeNO2Si: C: 64.64, H:
4.95, N: 3.28; found: C: 64.57, H: 5.32, N: 3.13. HRMS (ESI): Calcd for
C23H21FeNO2Si [M]þ: 427.0691, found: 427.0692. IR (KBr, cmꢁ1):
237.0367, found: 237.0365. IR (liquid film, cmꢁ1): 3303 (vs,
n^CeH),
3087 and 3004 (m,
897 (m and s,
n]CeH), 2140 (s, nC^C), 1629 (s, nC]C), 984 and
d
]CeH), 647 (s, d
^CeH). 1H NMR (300 MHz, CDCl3,
ppm):
d
6.44 (dd, 1H, 3JH,H¼10 and 18 Hz, eHC]CH2), 5.39 (dd, 1H,
3JH,H¼18 Hz and JH,H¼1 Hz, eHC]CH2 trans), 5.15 (dd, 1H,
3JH,H¼10 Hz and 2JH,H¼1 Hz, eHC]CH2 cis), 4.37 (m, 4H, C5H4), 4.28
and 4.16 (2ꢂ t, 2ꢂ 2H, 3JH,H¼2 Hz, C5H4), 2.77 (s, 1H, ^CH). 13C{1H}
2
NMR (125 MHz, CDCl3, ppm): d 133.4 (s, ]CH2), 112.1 (s, eC]), 84.8
(s, Cquat C5H4), 82.1 (s, C^CH), 73.9 (s, C^CH), 72.9, 71.3, 70.8 and
68.6 (4ꢂ s, C5H4), 64.8 (s, Cquat C5H4).
4.1.7. 10-Ethynyl-1-formylferrocene (7).33
4.1.7.1. With TBAF. 10-Trimethylsilylethynyl-1-formylferrocene
(9; 0.155 g, 0.50 mmol) was dissolved in THF (5 mL), cooled to 0 ꢀC
and TBAF (0.75 mL of a 1.0 M solution in THF, 0.75 mmol) was added
dropwise. After 1 h of stirring at room temperature, the reaction
mixture was quenched with water (0.50 mL), concentrated under
reduced pressure and worked up as usual. The resulting oil was
adsorbed onto silica and chromatographed (silica gel, 2.5ꢂ20 cm).
The orange band containing 7 eluted with hexanes/Et2O (2:1) was
collected. Solvents were removed by rotary evaporation and the dark
red oil dried in vacuo to give a red wax (0.075 g, 63%).
2203 (s, nC^C(Ar)), 2144 (s, nC^CðSiMe Þ), 1508 and 1342 (s, nNO2), 1250
3
(m, nSieC), 850 (vs, dAr para substituted). 1H NMR (300 MHz, CDCl3,
ppm):
d
8.22 (d, 2H, 3JH,H¼6 Hz, C6H4), 7.62 (d, 2H, 3JH,H¼6 Hz, C6H4),
4.53, 4.48, 4.35, and 4.28 (4ꢂ s, 8H, C5H4), 0.20 (s, 9H, SiMe3). 13C{1H}
NMR (125 MHz, CDCl3, ppm):
d 146.5 (s, Cipso C6H4NO2), 131.9 (s,
Cortho C6H4NO2), 131.0 (s, Cpara C6H4NO2), 123.6 (s, Cmeta C6H4NO2),
102.9 (s, eC^C(SiMe3)), 94.2 (s, (Ar)C^Ce), 91.8 (s, eC^C(SiMe3)),
84.9 (s, eC^C(Ar)), 73.7, 73.6, 72.1, and 71.1 (4ꢂ s, C5H4), 66.7 (s, Cquat
C5H4), 65.0 (s, Cquat C5H4), 0.2 (s, SiMe3).
4.1.7.2. With methanolic KOH. Aqueous KOH (0.4 mL of a 2.50 M
solution, 1.0 mmol) was added dropwise to a cooled (0 ꢀC) solution
of 10-trimethylsilylethynyl-1-formylferrocene (0.155 g, 0.50 mmol)
in MeOH (25 mL). The reaction mixture was allowed to warm to
room temperature slowly with the cold bath in place, and then
stirred 24 h at room temperature, and poured into water (50 mL).
After a standard work up and purification as described above,
0.085 g (71%) of the title compound was obtained. Rf (hexanes/Et2O
[2:1]): 0.36.
4.1.5. 10-Trimethylsilylethynyl-1-ethenylferrocene (12). Methyltriphen-
ylphosphonium bromide (1.50 g, 4.20 mmol) was suspended in THF
(25 mL), cooled to 0 ꢀC and treated with n-BuLi (2.50 mL, 4.0 mmol,
1.60 M solution in hexanes) at a rate of approximately 0.5 mL per
minute. After 30 min of stirring at
0 a solution of
ꢀC,
HRMS (EI) calcd. for C13H10FeO [M]þ: 238.0081, found:
10-trimethylsilylethynyl-1-formylferrocene (9; 0.620 g, 2.0 mmol) in
THF (5 mL) was added dropwise over 10 min, the cooling bath was
removed and the reaction mixture stirred for 16 h at room
temperature. Hydrolysis with water (25 mL) and standard work up
furnished an orange oil, which was chromatographed (silica gel,
4ꢂ20 cm) using a gradient elution from pure hexanes to hexanes/
Et2O (98:2). The orange band was collected and solvent removed by
rotary evaporation to give 12 as an orange solid (0.587 g, 95%), which
was dried in vacuo after being solidified by standing at ꢁ20 ꢀC for
16 h. Rf (hexanes): 0.27. Mp: <45 ꢀC. Elemental Analysis Calcd for
C17H20FeSi: C: 66.23, H: 6.54; found: C: 66.47, H: 6.15. HRMS (ESI):
Calcd for C17H20FeSi [M]þ: 308.0683, found: 308.0682. IR (KBr,
238.0078. IR (liquid film, cmꢁ1): 3283 (s,
d
^CeH), 2854 (m, nC(O)eH),
^CeH). 1H NMR (300 MHz,
9.96 (s, 1H, CHO), 4.84, 4.64, 4.56, and 4.31 (4ꢂ s, 4ꢂ
2H, C5H4), 2.82 (s, 1H, ^CH). 13C{1H} NMR (125 MHz, CDCl3, ppm):
193.6 (s, CHO), 80.7 (s, C^CH), 80.2 (s, Cquat C5H4), 75.6 (s, C^CH),
2109 (m, nC^C), 1683 (s, nC]O), 654 (m,
CDCl3, ppm):
d
d
d
75.2, 73.2, 71.3, and 60.3 (4ꢂ s, C5H4), 66.3 (s, Cquat C5H4). No ac-
curate elemental analysis of 7 could be obtained due its slow
decomposition.
4.1.8. 1,10-(4-Methoxy-1-butenylene)ferrocene (13). 1-Trimethylsilyle-
thynyl-10-ethenylferrocene (12; 0.154 g, 0.50 mmol) was dissolved
in MeOH (25 mL), cooled to 0 ꢀC, and aqueous KOH (0.40 mL of
a 2.50 M solution, 1.0 mmol) was added dropwise. The reaction
mixture was allowed to warm to room temperature slowly with the
cold bath in place, and then stirred for 24 h and poured into water
(50 mL). After a standard work up, the yellow oil was purified by
preparative TLC (silica, hexanes/Et2O [95:5]). The yellow band, Rf:
0.26, was collected, taken-up into Et2O and evaporated to dryness.
Recrystallization of the residue from aqueous ethanol yielded 13
(0.127 g, 87%) as yellow needles. Rf (hexanes/Et2O [95:5]): 0.18. Mp:
76 ꢀC. Elemental Analysis Calcd for C15H16FeO$¼H2O: C: 66.08, H:
6.10; found: C: 66.37, H: 5.93. HRMS (ESI): Calcd for C15H16FeO [M]þ:
268.0550, found: 268.0548. IR (KBr, cmꢁ1): 3078 and 3006 (m,
nHeC]), 2808 (m, nHeC OMe), 1646 (m, nC]C), 1088 (s, nCeO). 1H NMR
cmꢁ1): 3088 and 3005 (m,
1246 (s, nSieC), 926 and 842 (s,
n
]CeH), 2147 (s, nC^C), 1630 (m, nC]C),
d
]CeH). 1H NMR (300 MHz, CDCl3,
3
ppm):
d
6.42 (dd, 1H, JH,H¼12 and 18 Hz, eHC]CH2), 5.36 (dd, 1H,
3JH,H¼18 Hz and JH,H¼1 Hz, eHC]CH2 trans), 5.13 (dd, 1H,
3JH,H¼12 Hz and 2JH,H¼1 Hz, eHC]CH2 cis), 4.35 (m, 4H, C5H4), 4.24
and 4.13 (2ꢂ t, 2ꢂ 2H, 3JH,H¼2 Hz, C5H4), 0.23 (s, 9H, SiMe3). 13C{1H}
2
NMR (125 MHz, CDCl3, ppm):
d 133.4 (s, ]CH2), 112.0 (s, eC]),
103.6 (s, C^C(SiMe3)), 90.9 (s, C^C(SiMe3)), 84.8 (s, Cquat C5H4),
72.9, 70.7, 69.9, and 68.6 (4ꢂ s, C5H4), 65.9 (s, Cquat C5H4), 0.3 (s, SiMe3).
4.1.6. 10-Ethenyl-1-ethynylferrocene (6). TBAF (0.75 mL of a 1.0 M
solution in THF, 0.75 mmol) was added dropwise to 10-trime-
thylsilylethynyl-1-ethenylferrocene (12) in THF (5 mL) at 0 ꢀC. The

3322
G. Grelaud et al. / Tetrahedron 69 (2013) 3316e3322
Dong, T.-Y.; Lin, S.-F.; Chen, C.-P.; Yeh, S.-W.; Chen, H.-Y.; Wen, Y.-S. J. Organomet.
(300 MHz, CDCl3, ppm):
d
6.18 (d, 1H, 3JH,H¼12 Hz, C5H4eCH]CHe),
Chem. 2009, 694, 1529e1540; (d) Bruce, M. I.; Low, P. J.; Hartl, F.; Humphrey, P.
A.; de Montigny, F.; Jevric, M.; Lapinte, C.; Perkins, G. J.; Roberts, R. L.; Skelton,
B. W.; White, A. H. Organometallics 2005, 24, 5241e5255 and references
therein.
5.89 (td, 1H, 3JH,H¼9 and 12 Hz, C5H4eCH]CHe), 4.36 (m, 1H, C5H4),
4.28e4.18 (m, 5H, C5H4), 4.12 (m,1H, C5H4), 4.01 (m,1H C5H4), 3.55 (d,
1H, 3JH,H¼6 Hz, C5H4eCH(OMe)), 3.16 (s, 3H, OMe), 2.91 (td, 3JH,H¼9
and 12 Hz, 1H, H CH2), 2.50 (t, 1H, 3JH,H¼10 Hz, H CH2). 13C{1H} NMR
10. (a) Inouye, M.; Hyodo, Y.; Nakazumi, H. J. Org. Chem. 1999, 64, 2704e2710; (b)
Iftime, G.; Moreau-Bossuet, C.; Manoury, E.; Balavoine, G. G. A. Chem. Commun.
1996, 527e528.
(75 MHz, CDCl3, ppm):
d 129.1 (s, C5H4eCH]CHe), 127.5 (s,
11. Dachiele, E. A.; Aurora, A.; Bernardini, G.; Cattaruzza, F.; Flamini, A.; Pallavicini,
P.; Zanoni, R.; Decker, F. J. Electroanal. Chem. 2005, 579, 133e142.
12. Benkeser, R. A.; Fitzgerald, W. P. J., Jr. J. Org. Chem. 1961, 26, 4179e4180.
13. Polin, J.; Schottenberger, H. Org. Synth. 1998, 9, 411e415.
14. Buchmeiser, M.; Schottenberger, H. J. Organomet. Chem. 1992, 436, 223e230.
15. Doisneau, G.; Balavoine, G. B.; Fillebeen-Khan, T. J. Organomet. Chem. 1992, 425,
113e117.
C5H4eCH]CHe), 84.0 and 81.9 (2ꢂ s, Cquat C5H4), 76.1 (s,
C5H4eCH(OMe)e), 70.3, 70.2, 70.0, 69.3, 68.9, 68.7, 68.5 and 66.9 (8ꢂ
s, C5H4), 56.1 (s, OMe), 35.0 (s, CH2).
Acknowledgements
16. (a) Wu, J. S.; Chi, C. Y.; Wang, X. H.; Zhao, X. J.; Li, J.; Wang, F. S. Chin. Chem. Lett.
2001, 12, 387e390; (b) Tsuboya, N.; Hamasaki, R.; Ito, M.; Mitsuishi, M.;
Miyashita, T.; Yamamoto, Y. J. Mater. Chem. 2003, 13, 511e513.
17. Wurst, K.; Elsner, O.; Schottenberger, H. Synlett 1999, 833e834.
18. Pudelski, J. K.; Callstrom, M. R. Organometallics 1992, 11, 2757e2759.
19. Bunz, U. H. F. J. Organomet. Chem. 1995, 494, C8eC11.
20. Pudelski, J. K.; Callstrom, M. R. Organometallics 1994, 13, 3095e3109.
21. Mamane, V. Mini-Rev. Org. Chem. 2008, 5, 303e312.
22. Butler, I. R.; Boyes, A. L.; Kelly, G.; Quayle, S. C.; Herzig, T.; Szewczyk, J. Inorg
Chem. Commun. 1999, 2, 403e406.
S. Sinbandhit (CRMPO e UMR 6226) is kindly acknowledged for
NMR assistance. G.G. thanks Region Bretagne and the Australian
Research Council (ARC) for PhD scholarships. The CNRS (PICS pro-
gram No. 5676), and the ANR (09-BLAN-0109), are acknowledged
for financial support. M.G.H. holds an ARC Australian Professorial
Fellowship and M.P.C. holds an ARC Australian Research Fellowship.
23. (a) Schlijgl, K.; Steyrer, W. Monatsh. Chem. 1965, 96, 1520e1535 for a recent
study of the deprotection of 3 see: Yoshino, J.; Shimizu, R.; Hayashi, N.; Higuchi,
H. Bull. Chem. Soc. Jpn. 2011, 84, 110e118 and references therein.
Supplementary data
Copiesof 1HNMR and13C NMR spectroscopicdataof1, 6, 7 9,10,11,
12, and 13,1H/1H COSYof 13, CV trace for 1, 6, 7, 9,11,12, and 13 can be
found, in the online version. Supplementary data related to this ar-
ticle can be found at http://dx.doi.org/10.1016/j.tet.2013.01.093.
€
€
24. Ma, J.; Kuhn, B.; Hackl, T.; Butenschon, H. Chem.dEur. J. 2010, 1859e1870.
€
25. (a) Fortage, J.; Boixel, J.; Blart, E.; Hammarstrom, L.; Becker, H. C.; Odobel, F.
ꢀ
Chem.dEur. J. 2008, 14, 3467e3480; (b) Nierengarten, J.-F.; Zhang, S.; Gegout,
A.; Urbani, M.; Armaroli, N.; Marconi, G.; Rio, Y. J. Org. Chem. 2005, 70,
7550e7557.
26. (a) Sonogashira, K.; Tohda, Y.; Hagihara, N. Tetrahedron Lett. 1975, 50,
4467e4470; (b) Sonogashira, K. In Handbook of Organopalladium Chemistry for
Organic Synthesis; Negishi, E.-I., De Meijere, A., Eds.; Wiley and Sons: New York,
NY, 2002; pp 493e530.
References and notes
27. (a) Corey, E. J.; Fuchs, P. L. Tetrahedron Lett. 1972, 3769e3772; (b) Li, J. J. Name
Reactions; Springer: Berlin, Germany, 2008, pp 160e161.
28. Xu, G.-L.; Xi, B.; Updegraff, J. B.; Protasiewicz, J. D.; Ren, T. Organometallics 2006,
25, 5213e5215.
29. Netherton, M. R.; Fu, G. C. Org. Lett. 2001, 3, 4295e4298.
30. The failure of P(t-Bu)3/[PdCl2(PhCN)2] to produce even trace amounts of 9 from
the bromo analogue of 8 is surprising, particularly because this catalyst is
known to activate highly electron-deficient substrates, see: Littke, A. F.;
Schwarz, L.; Fu, G. C. J. Am. Chem. Soc. 2002, 124, 6343e6348 and references
therein.
1. (a) Kealy, T. J.; Pauson, P. L. Nature 1951, 168, 1039e1040; (b) Miller, S. A.;
Tebboth, J. A.; Tremaine, J. F. J. Chem. Soc. 1952, 632e635; (c) Wilkinson, G.;
Rosenblum, M.; Whiting, M. C.; Woodward, R. B. J. Am. Chem. Soc. 1952, 74,
2125e2126; (d) Fischer, E. O.; Pfab, W. Z. Naturforsch. 1952, 7B, 377e379.
2. See for example: (a) Togni, A.; Hayashi, T. Ferrocenes; VCH: Weinheim, Ger-
many, 1995; (b) Nguyen, P.; Gomez-Elipe, P.; Manners, I. Chem. Rev. 1999, 99,
1515e1548; (c) Stepnicka, P. Ferrocenes: Ligands, Materials and Biomolecules;
Wiley: Chichester, 2008.
3. For recent examples, see: (a) Broderick, E. M.; Guo, N.; Vogel, C. S.; Xu, C.;
Sutter, J.; Miller, J. T.; Meyer, K.; Mehrkhodavandi, P.; Diaconescu, P. L. J. Am.
Chem. Soc. 2011, 133, 9278e9281; (b) Tropiano, M.; Kilah, N. L.; Morten, M.;
Rahman, H.; Davis, J. J.; Beer, P. D.; Faulkner, S. J. Am. Chem. Soc. 2011, 133,
11847e11849; (c) Rochford, J.; Rooney, A. D.; Pryce, M. T. Inorg. Chem. 2007, 46,
7247e7249; (d) Gregson, C. K. A.; Gibson, V. C.; Long, N. J.; Marshall, E. L.;
Oxford, P. J.; White, A. J. P. J. Am. Chem. Soc. 2006, 128, 7410e7411; (e) Allgeier,
A. M.; Mirkin, C. A.; Liable-Sands, L. M.; Yap, G. P. A.; Rheingold, A. L. Angew.
Chem., Int. Ed. 1998, 37, 894e908.
31. (a) Wittig, G.; Geissler, G. Liebigs Ann. Chem. 1953, 580, 44e57; (b) Wittig, G.;
Schollkopf, U. Chem. Ber. 1954, 87, 1318e1330; (c) Maryanoff, B. E.; Reitz, A. B.
Chem. Rev. 1989, 89, 863e927.
32. Rausch, M. D.; Siegel, A. J. Organomet. Chem. 1968, 11, 317e324.
€
33. Schottenberger, H.; Lukassser, J.; Reichel, E.; Muller, A. G.; Steiner, G.; Kopacka,
H.; Wurst, K.; Ongania, K. H.; Kirchner, K. J. Organomet. Chem. 2001, 637-639,
558e576.
34. (a) Gubin, S. A. Pure Appl. Chem. 1970, 24, 463e487; (b) Lu, S.; Strelets, V. V.;
Ryan, M. F.; Pietro, W. J.; Lever, A. B. P. Inorg. Chem. 1996, 35, 1013e1023; (c)
Britton, W. E.; Kashyap, R.; El-Hashash, M.; El-Kady, M.; Herberhold, M. Or-
ganometallics 1986, 5, 1029e1031.
35. A linear correlation of the oxidation potential as a function of the sum of the
Hammett constant of the substituents of the ferrocene derivatives reported
here can be established, with R2 ¼ 0.97.
4. (a) Green, M. L. H.; Marder, S. R.; Thompson, M. E.; Brandy, J. A.; Bloor, D.;
Kolinsky, P. V.; Jones, R. J. Nature 1987, 330, 360e362; (b) Marder, S. R. In In-
organic Materials; Bruce, D. W., O’Hare, D., Eds.; Wiley: Chichester, New York,
Brisbane, Toronto, Singapore, 1992; pp 115e164; (c) Barlow, S.; Marder, S. R.
Chem. Commun. 2000, 1555e1562.
5. (a) Whittall, I. R.; McDonagh, A. M.; Humphrey, M. G.; Samoc, M. Adv. Orga-
nomet. Chem. 1998, 42, 291e362; (b) Whittall, I. R.; McDonagh, A. M.; Hum-
phrey, M. G.; Samoc, M. Adv. Organomet. Chem. 1999, 43, 349e405; (c) See also
the chapter written by Heck, J.; Dede, M., pp 319e392 of ref 2c.
6. (a) Kondo, T.; Horiuchi, S.; Yagi, I.; Ye, S.; Uosaki, K. J. Am. Chem. Soc. 1999, 121,
391e398; (b) Malaun, M.; Reeves, Z. R.; Paul, R. L.; Jeffery, J. C.; McCleverty, J. A.;
Ward, M. D.; Asselberghs, I.; Clays, K.; Persoons, A. Chem. Commun. 2001,
49e50; (c) Malaun, M.; Kowallick, R.; McDonagh, A. M.; Marcaccio, M.; Paul, R.
L.; Asselberghs, I.; Clays, K.; Persoons, A.; Bildstein, B.; Fiorini, C.; Nunzi, J.-M.;
Ward, M. D.; McCleverty, J. A. Dalton Trans. 2001, 3025e3038.
36. Hansch, C.; Leo, A.; Taft, R. W. Chem. Rev. 1991, 91, 165e195.
37. Kuwana, T.; Bublitz, D. E.; Hoh, G. L. K. J. Am. Chem. Soc. 1960, 82, 5811e5817.
38. Denis, R.; Toupet, L.; Paul, F.; Lapinte, C. Organometallics 2000, 19, 4240e4251.
39. In the case of 6 (Supplementary data), the loss of reversibility is consistent with
the irreversible oxidation reported for 1,10-diethenylferrocene18 and may pos-
sibly result from polymerization of the electrogenerated ferrocenyl radical,
since ethenylferrocene is known to be easily polymerized via a free radical
process.40 Electrocyclization of the radical cation of 6 at the electrode surface
forming a [4]-ferrocenophane is another possible explanation for the loss of
reversibility.
7. (a) Hurst, S. K.; Humphrey, M. G.; Morrall, J. P.; Cifuentes, M. P.; Samoc, M.;
Luther-Davies, B.; Heath, G. A.; Willis, A. C. J. Organomet. Chem. 2003, 670,
56e65; (b) Grelaud, G.; Cifuentes, M. P.; Schwich, T.; Argouarch, G.; Petrie, S.;
Stranger, R.; Paul, F.; Humphrey, M. G. Eur. J. Inorg. Chem. 2012, 65e75.
8. Gauthier, N.; Argouarch, G.; Paul, F.; Humphrey, M. G.; Toupet, L.; Ababou-
Girard, S.; Sabbah, H.; Hapiot, P.; Fabre, B. Adv. Mater. 2008, 20, 1952e1957.
9. For selected organometallic examples, see for instance: (a) Packheiser, R.;
40. (a) Arimoto, F. S.; Haven, A. C., Jr. J. Am. Chem. Soc. 1955, 77, 6295e6297; (b)
Baldwin, M. G.; Johnson, K. E. J. Polym. Sci., Part A-1: Polym. Chem. 1967, 5,
2091e2098.
41. Cummings, S. P.; Savchenko, J.; Ren, T. Coord. Chem. Rev. 2011, 255, 1587e1602.
42. Komiya, S.; Ozawa, F. Synthesis of Organometallic Compounds; Wiley: Chichester,
United Kingdom, 1997.
€
Ecorchard, P.; Ruffer, T.; Lang, H. Chem.dEur. J. 2008, 14, 4948e4960; (b) Fan, Y.;
43. Connelly, N. G.; Geiger, W. E. Chem. Rev. 1996, 96, 877e910.
Liu, Y. P.-O.; Fanwick, P. E.; Ren, T. Organometallics 2009, 28, 3959e3962; (c)