The synthesis and characterisation of novel ferrocenyl polyphenylenes

Article abstract of DOI:10.1039/c2dt30542a

This work describes the synthesis and characterisation of a new series of polyphenylenes with up to four ferrocenyl moieties. The synthetic route involves the preparation of a number of novel precursors. Cyclopentadienones, generated from the two-fold Knoevenagel condensation of di-ferrocenyl propanones and diketones, are used in [2 + 4] Diels-Alder cycloadditions with appropriately substituted acetylenes. 13 is amongst the compounds isolated. It is the largest ferrocenyl-supported polyaromatic hydrocarbon (PAH) to date. Prepared via a Sonogashira cross-coupling reaction between ethynyl-Fc and iodo-HBC, it comprises a hexa-peri-hexabenzocoronene (HBC) core linked via acetylene to a ferrocenyl unit (Fc). The electrochemical and absorption properties of the ferrocenyl-polyphenylenes and the fully conjugated 13 are discussed. The NLO data for 13, determined by hyper Rayleigh scattering techniques, are compared to those of similar fulleryl-based compounds in the literature. The Royal Society of Chemistry 2012.

Full text of DOI:10.1039/c2dt30542a

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PAPER
The synthesis and characterisation of novel ferrocenyl polyphenylenes†
Dilwyn J. Roberts,a Deanne Nolan,a Gearóid M. Ó Máille,a Graeme W. Watson,a Anu Singh,b
Isabelle Ledoux-Rakb and Sylvia M. Draper*a
Received 6th March 2012, Accepted 20th May 2012
DOI: 10.1039/c2dt30542a
This work describes the synthesis and characterisation of a new series of polyphenylenes with up to four
ferrocenyl moieties. The synthetic route involves the preparation of a number of novel precursors.
Cyclopentadienones, generated from the two-fold Knoevenagel condensation of di-ferrocenyl propanones
and diketones, are used in [2 + 4] Diels–Alder cycloadditions with appropriately substituted acetylenes.
13 is amongst the compounds isolated. It is the largest ferrocenyl-supported polyaromatic hydrocarbon
(PAH) to date. Prepared via a Sonogashira cross-coupling reaction between ethynyl-Fc and iodo-HBC,
it comprises a hexa-peri-hexabenzocoronene (HBC) core linked via acetylene to a ferrocenyl unit (Fc).
The electrochemical and absorption properties of the ferrocenyl-polyphenylenes and the fully
conjugated 13 are discussed. The NLO data for 13, determined by hyper Rayleigh scattering
techniques, are compared to those of similar fulleryl-based compounds in the literature.
Introduction
As a robust organometallic electron-donor group with well-
established substitution chemistry1 the ferrocenyl-moiety has
been incorporated into new molecular materials exhibiting non-
linear optical (NLO)2 and ferromagnetic properties.3 The bulk
properties of a molecular material can be heavily influenced in
the solid-state by its packing arrangement. For this reason, com-
pounds combining a ferrocene donor and a planar polycyclic
aromatic hydrocarbon (PAH), capable of π-stacking, are of con-
siderable interest. PAHs are useful as linking groups in donor–
Fig. 1 The structures of the two known PAHs incorporating a ferro-
cene moiety 1,2-ferrocenyl-pyrenyl-ethene (I) and tetra-peri-benzo-peri-
ferrocenyl-coronene (II).
acceptor organometallic systems because they are planar, rela-
tively rigid with a fixed geometry and have various isomeric
ethynylated cyclobutadienes,4–6 η6-tricarbonyl chromium7 and
positions through which organometallic moieties may be bound.
η6-[Rh(COD)]+ hexa-peri-hexabenzocoronene (HBC)8 and
Their highly delocalised π-systems with small HOMO–LUMO
HBCs incorporating σ-bonded Pt(II) acetylides.9
energy separations and low vacant π*-orbitals can facilitate elec-
To date there are just two compounds reported where ferro-
tronic communication between donors and acceptors. Although
cene is attached to an all-benzenoid PAH, one of which com-
large polycyclic materials incorporating over 200 carbon atoms
prises four fused benzene rings,3 the other eight (Fig. 1).10 Both
come some way short of the thirteen fused benzene rings found
have been characterised, very few of these systems are organo-
metallic. Known examples include Bunz’s cobalt-containing
in HBC (Fig. 2). The L-shaped 1,2-ferrocenyl-pyrenyl-ethene (I)
has fascinating solid state electrical conductivity properties3
aSchool of Chemistry, University of Dublin, Trinity College, College
Green, Dublin 2, Ireland. E-mail: smdraper@tcd.ie;
whereas (II) with a single bond between the ferrocene moiety
and the PAH fragment offers limited communication between
Fax: +353-1-671-2826; Tel: +353-1-896-2026
the two end groups (Fig. 1).10
bLaboratoire de Photonique Quantique et Moléculaire (UMR CNRS
To combine the desirable features of both I and II we decided
to increase the size of the PAH platform and to introduce an
acetylene linker as an active pathway for electronic communi-
cation. Known ferrocenyl-acetylenes have been shown to have
considerable potential in NLO, catalysis, as models of charge
transfer and in the synthesis of more complex molecules with
well-defined magnetic and electronic properties.4,11–13 Given
these considerations, 13 became a desirable target molecule
(Fig. 2).
8537), Institut d’Alembert, ENS Cachan, 61 Avenue du Président
Wilson, 94235 Cachan, Cedex, France
†Electronic supplementary information (ESI) available: 1H NMR
(400 MHz) spectra recorded in CDCl3 of 4, 7, 8, 9, 10, 11, 12,
iodo-HBC and 1,2-bis(p-ferrocenylphenyl)acetylene. The experimental
(+)-MALDI-TOF spectra of 13 and (MH)+ simulated isotopic distri-
bution pattern. Schematic and experimental details for the total synthesis
of 1,2-bis(p-ferrocenylphenyl)acetylene. Tabulated electronic charge of
the ethyne, cyclopentadienyl (Cp), ferrocence and HBC components,
ethynyl ferrocene and methyl derivative of 13. See DOI:
10.1039/c2dt30542a
8850 | Dalton Trans., 2012, 41, 8850–8860
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ferrocene units and in some cases nitrogen heteroatoms to
aid solubility, and/or electron-rich methoxy groups.14,15 It
was hoped that such derivatisation would yield highly conju-
gated systems with moderately electron-donating and electron-
accepting regions.
Results and discussion
The ferrocene moiety was incorporated into the polyphenylene
systems by synthesising a library of novel ferrocene-containing
precursors, suitable for subsequent [2 + 4] Diels–Alder cyclo-
addition and conversion to aromatic PAHs via cyclodehydro-
genation. The synthesised molecules contained up to four
Synthesis of heteroatom-containing polyphenylenes 10, 11
and 12
In order to incorporate multiple ferrocene moieties into the poly-
phenylene systems, di-ferrocenyl mono-ketone (4) was syn-
thesised (Scheme 1). The initial step involved the synthesis of 1
via the diazotization reaction between ferrocene (FcH) and
4-aminobenzylalcohol. The bromination of the hydroxyl group
was achieved using phosphorous tribromide in dichloromethane
which yielded 2, in almost quantitative yield. The new com-
pound di-ferrocenyl ketone 4 was prepared by a bi-phasic, iron
Fig. 2 Structure of 2-ethynylferrocenyl-5,8,11,14,17-penta-tert-butyl-
hexa-peri-hexabenzocoronene (13).
Scheme 1 The synthetic route to polyphenylenes 10, 11, and 12. (i) H2SO4/H2O, sodium nitrite, 4-aminobenzylalcohol, HCl, Cu powder, 24 h, 1
(31%). (ii) PBr3, CH2Cl2, 0 °C, 30 min, 2 (94%), (3 purchased directly). (iii) Ca(OH)2, Bu4N(HSO4), Fe(CO)5, CH2Cl2/H2O, 6 h, 4 (58%), 5 (65%).
(iv) H2SO4/H2O, sodium nitrite, 4-aminobenzonitrile, HCl, Cu powder, 24 h, (35%). (v) DIBAL, toluene, RT, 6 h, (91%). (vi) NaCN, water/ethanol,
reflux 1 h, 6 (59%). (vii) MnO2, CHCl3, reflux, 24 h, 7 (88%). (viii) KOH, C2H5OH/CH2Cl2, 18 h (8)/3 h (9), 8 (63%), 9 (64%). (ix) Dipyrimidyl-
acetylene, benzophenone, 200 °C, 18 h, 10 (54%), 11 (58%). (x) 1,2-Bis(p-ferrocenylphenyl)acetylene, benzophenone, 190 °C, 18 h, 12 (18%).
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Scheme 2 Synthesis of 13 from iodo-HBC, (i) ethynyl ferrocene,
Pd(PPh3)4, Et3N–toluene (1 : 2), 70 °C, 18 h, (77%).
pentacarbonyl mediated coupling reaction. The methoxy-substi-
tuted 1,3-diaryl-2-propanone (5) was synthesised in a similar
vein in 65% yield from the commercially available 3,-5-
dimethoxybenzyl bromide (3). As well as the di-ferrocenyl
mono-ketone (4) the di-ferrocenyl di-ketone (7) was also pre-
pared. This was achieved in four steps from ferrocene as illus-
trated in Scheme 1. The first step involved a diazotization
reaction between ferrocene and 4-aminobenzonitrile16 to give
4-ferrocenylbenzonitrile (35% yield), for conversion to 4-ferro-
cenylbenzaldehyde in almost quantitative yield. The keto-alcohol
7 (also novel) was synthesised via the benzoin condensation of
two molecules of 4-ferrocenylbenzaldehyde.
The two cyclopentadienones 8 and 9 were prepared via a two-
fold Knoevenagel condensation reaction between 7 and the corre-
sponding mono-ketones (4 and 5). Both condensations were
carried out in ethanolic potassium hydroxide solutions. Cyclopen-
tadienone 8 was found to be quite unstable as a solid and particu-
larly unstable in solution. Polyphenylenes 10 and 11 were
obtained as orange crystalline solids via the Diels–Alder [2 + 4]-
cycloaddition of 8 and 9, respectively, with dipyrimidyl acetylene.
To expand the library of possible compounds, 1,2-bis(p-ferro-
cenylphenyl)acetylene was successfully synthesised (Scheme S1,
ESI†) using a route that differs from that published by Rathore
et al.17 and subsequently used in a [2 + 4] Diels–Alder cyclo-
addition with 9 to give tetra-ferrocenyl polyphenylene 12.
Fig. 3 1H NMR spectrum of 13 (CDCl3, RT, 600 MHz).
direction was required. Müllen et al.18,19 amongst others9,20 have
shown that halogen atoms incorporated into PAH are labile
enough to undergo palladium catalysed coupling reactions. It
was decided to use iodo-HBC9,20 which would benefit from the
efficient nature of the Scholl reaction for the C–C bond for-
mation in all-carbon polyphenylenes and simultaneously provide
a predetermined site for the ferrocene moiety. Ethynyl ferrocene
was synthesised according to literature procedures,38 and was
cross-coupled with iodo-HBC using Sonogashira methodology
to give 13 (Scheme 2).
The 1H NMR spectrum of 13 consists of six well-defined
singlets in the aromatic region due to the presence of a C2 axis
of symmetry which renders half the protons magnetically equiv-
alent (Fig. 3). The ferrocenyl region exhibits the expected three
signals corresponding to the two non-equivalent proton environ-
ments of the substituted cyclopentadienyl ring and the one
proton environment of the protons on the unsubstituted cyclo-
pentadienyl ring. In the aliphatic region three distinct signals are
visible, integrating in the expected 1 : 2 : 2 ratio for the tert-butyl
groups.
1
The H NMR spectrum of 13 was readily assigned by various
NOE and 2D experiments using the clearly discernible signal for
the tert-butyl group H13. TOCSY experiments provided evi-
dence for the long range interactions between protons on adja-
cent rings and allowed a full assignment of the spectrum.
Attempted cyclodehydrogenation of polyphenylenes 10, 11 and 12
Attempts to cyclodehydrogenate ferrocenyl polyphenylenes 10
and 11 to form planar, ring-closed systems were unsuccessful,
yielding only black, insoluble and un-characterisable solids
indicative of complete decomposition. In an attempt to improve
on these results, polyphenylene 12 was produced (Scheme 1) to
incorporate electron-donating methoxy groups which are known
to activate C–C bond formation in cyclodehydrogenation reac-
tions. This did not improve the outcome of the attempted cyclo-
dehydrogenation which we believe to be a consequence of the
partial oxidative decomposition by Cu(II) of the exposed Fe
centre in tilted ferrocenyl moieties.6,10
Phenyl groups prefer to associate in either an edge-to-edge or
face-to-face orientation (π–π stacking).21 Such interactions have
been the subject of a number of investigations21–23 that have
attempted to address the role of molecular geometry22,23 and
electrostatic factors in promoting aromatic association.24–27 The
1H NMR signals of the aromatic protons of 13 were found to be
concentration dependent, especially the upfield protons H7, H8
and H9, which are closest to the ferrocene moiety (Fig. 4). At
ambient temperature in CDCl3 the chemical shift for H7 varied
greatly from δ 8.90 ppm (7.40 × 10−3 M) to δ 9.19 ppm (0.06 ×
10−3 M) suggesting a significant degree of molecular aggrega-
tion. It has been shown by Moore et al.28 that ethynyl moieties
can form π–π interactions with PAHs and macrocycles. The
greatest overlap of π orbitals in 13 is likely to be in the region
closest to the electron donating ferrocene, hence the movement
of H7 in the 1H NMR spectrum.
Synthesis and spectroscopic characterisation of
2-ethynylferrocenyl-5,8,11,14,17-penta-tert-butylhexa-
peri-hexabenzocoronene (13)
As a consequence of the unsuccessful cyclodehydrogenation of
the ferrocene-containing 10, 11 and 12, a change of synthetic
8852 | Dalton Trans., 2012, 41, 8850–8860
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Table 1 The UV-Vis data for ferrocene (FcH) and compounds 10–13
in toluene (∼10−5 M)
Low energy d–d
transition
Compound λmax/nm, (ε/L mol−1 cm−1 ×103)
FcH
10
11
12
13
325 (0.5)
355 (12.6)
354 (12.1)
350 sh (1.7)
334 (27.3), 350 (61.7), 366 (138.7),
396 (50.7), 414 (19.0)
439 (0.5)
443/5 (2.8)
440 (2.6)
445 (0.3)
ca. 440
1
Fig. 4 The concentration dependence of the H NMR aromatic signals
of compound 13 (CDCl3, RT, 600 MHz): (i) 0.06 mmol dm−3, (ii)
0.12 mmol dm−3, (iii) 0.23 mmol dm−3, (iv) 0.46 mmol dm−3, (v)
0.93 mmol dm−3, (vi) 1.85 mmol dm−3, (vii) 3.70 mmol dm−3, (viii)
7.40 mmol dm−3
.
UV-Vis absorption spectroscopy of polyphenylenes 10–12 and
Fc-ethynyl-HBC (13)
Electronic absorption spectra of ferrocene and substituted ferro-
cenes reveal that in ferrocene the metal centred dz2 orbital is gen-
erally the HOMO, a combination of the dxz and dyz is the LUMO
and the LUMO + 1 has a proposed composition of the dxy and
Fig. 5 The UV-Vis absorption spectra of 13 and 14 (inset) recorded in
toluene (10−5 M).
2
2 29,30
dx –y .
The absorption around λ 440 nm in ferrocene is thus
1
1
assigned to the E1g ← A1g [LUMO ← HOMO] ligand field
(LF) transition and the higher energy band around λ 325 nm to
the 1E2g ← 1A1g [(LUMO + 1) ← HOMO] LF transition. Substi-
tution of a Cp ring in ferrocene with conjugated acceptor groups
is generally followed by drastic changes in absorption
spectra.29,30 LF, otherwise known as “d–d” transitions, in orga-
nometallics are highly covalent and the electronic transitions
involving d-orbitals are sensitive to ligand binding.31
This weak d–d transition is evident between λ 440–445 nm
(Table 1) for each of the ferrocenyl-polyaromatic molecules pre-
pared here (polyphenylenes 10–12 and Fc-HBC (13)) with weak
extinction coefficients indicative of the forbidden nature of the
transition (ε = molar extinction coefficient, L mol−1 cm−1). The
minor variation in the energy of this band reveals the weak
influence that the nature of the substituent has on the transition.
For PAHs the dominant π–π* transitions usually occur in the λ
300–420 nm region and are highly structured and well-resolved
because of the delocalised and rigid nature of the molecular plat-
form. The all-carbon HBC, hexa-tert-butyl-hexa-peri-hexaben-
zocoronene (14) was synthesised7 for direct comparison with 13
(Fig. 5).
The UV-Vis spectra of 13 and 14 have similar profiles;
however as expected the absorptions in 13 are slightly red-
shifted. Both spectra show the three-band profile (α, β and p),
typical of aromatic hydrocarbons. The β-band appears at λ
366 nm and corresponds to the electronic interaction between the
benzenoid rings of the PAH. The p-bands appear at λ 396 nm for
13 (5 nm red shift compared to 14) and involve the localisation
of the π-electrons in the excited state. The red-shifted band in 13
at λ 414 nm is assigned to the 0–0, 1(π, π*) transition, with
Fig. 6 Normalised UV-Vis absorption spectra of ferrocenyl-polyphe-
nylenes 10–12 recorded in toluene (∼10−5 M) with inset lower energy
region.
enhanced molar absorptivity compared to 14 due to the lifting of
molecular symmetry (D6h to C2v). The red-shift of these bands is
indicative of an extension to the π-system of the HBC core,
facilitated by the ethynyl linkage.
In contrast, the absorption spectra of polyphenylenes 10–12
are dominated by strong, high-energy absorption bands between
λ 300–350 nm attributable to ππ* and nπ* transitions centred on
the hexa-arylbenzene core (Fig. 6). Most probably the absence
of effective conjugation between the ferrocenyl moiety and the
polyphenylene occurs due to steric hindrance in the ground state.
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Table 2 Electrochemical data for ferrocenyl complexesa
Complex
E°/V
ΔEp/mV
10
11
12
13
(II)
+0.03
−0.01
−0.06
+0.14
+0.04
169
120
114
136
70
a Redox potentials are given in CH2Cl2 solution (1 mM), using a
platinum disc working electrode, Pt wire auxiliary electrode, Ag/Ag+
reference electrode, 100 mV s−1 scan rate with 0.1 M Bu4NPF6 as
supporting electrolyte (V vs. Fc/Fc+). ΔEp is given by (Epa − Epc).
Fig. 7 HOMO of the methyl derivative of 13, calculated at the MO6/
6-31G(d,p) level.
This would impose a non-planar configuration of the bound Cp
and the phenyl ring of the hexa-arylbenzene and consequently
inefficient orbital overlap.
ferrocene, and the methyl derivative of 13 (methyl 13). Consist-
ent with its highly conjugated π-system HBC was found to have
the highest HOMO and lowest LUMO of the fragments con-
sidered. Ferrocene had the next highest HOMO and the next
lowest LUMO (with a significant part of the wavefunction on the
Fe) and ethyne had the lowest HOMO and the highest LUMO.
The energy of these frontier orbitals carried through to the
HOMO of methyl 13 which was found to be composed primar-
ily of the HBC HOMO containing significant contributions from
both the ethyne (the lowest HOMO as an isolated molecule) and
the Fe (Fig. 7).
While the HOMO provides information regarding the nature
of the highest energy orbital, it does not provide information
regarding the total charge redistribution. To assess this we
performed Mullikan analysis (Table S1†) which shows that on
going from ferrocene to ethynyl-ferrocene, the movement of
charge occurs from the Fe and the ethynyl group to the attached
cyclopentadienyl ring (Cp). (This is contrary to the commonly
held view of ethynyl as electron withdrawing.) The addition of
HBC increases the negative charge on the substituted cyclo-
pentadiene and indeed on the acetylene linker itself which
becomes integrated into an ethyne-HBC conjugated platform.
The net effect is to depopulate the Fe further (and marginally
depopulate the HBC).
Electrochemistry
The ferrocene/ferrocenium redox couple represents a strictly
reversible one-electron process, although in some cases reversi-
bility is lowered by the subsequent decomposition of the electro-
generated ferrocenium species.11 It gives information on any
changes in the distribution of electron density and HOMO
energies in a series of related compounds.11 The relevant electro-
chemical data for polyphenylenes 10–12 and Fc-HBC (13) and
for tetra-peri-benzo-peri-ferrocenyl-coronene (II) (structure pres-
ented in Fig. 1) as 1 mM dichloromethane solutions are com-
pared in Table 2.
These compounds are electrochemically active and in each
case, cyclic voltammetry in solution shows a single oxidation
peak corresponding to the Fe(II)/Fe(III) redox couple. The oxi-
dation potentials for 10–12 occur within the range −0.06 to
+0.03 V, quite similar to ferrocene itself. This indicates that the
electron density at the metal centre in these compounds, i.e. the
energy of the HOMO, does not vary significantly upon changing
substituents on the polyphenylene core. This is a consequence of
the limited communication through the single carbon–carbon
bond between the Fc moieties and the polyaromatic framework.
Compounds 13 and (II) are usefully compared as both consist of
a ferrocenyl moiety connected via a π-conjugated bridge to a
fused aromatic platform. For (II) the fully reversible redox
process was found to occur at +0.04 V (vs. Fc/Fc+). This is
anodically shifted compared to the quasi-reversible oxidation of
13 and is indicative of a comparative reduction in electron
density at the iron centre in 13 relative to (II), with the result that
its metal centre is comparatively more difficult to oxidise. The
acetylene-HBC unit has a considerable influence on the redox
properties of the Fe core which we explored using theoretical
methods.
The theoretical calculations show that the HOMO and LUMO
states are not spatially different, indicating no charge transfer
will occur upon excitation (assuming a primarily HOMO–
LUMO transition). This is consistent with the experimental
findings: i.e. no charge transfer in the ground state absorption
spectra and an increase in the oxidation potential on going from
ferrocene to 13.
NLO properties of 13
A number of organic compounds have been studied as possible
NLO materials as they offer some advantages over inorganic
crystals. In general, organic NLO compounds comprise a
bridged π-conjugation system and donor and acceptor end
groups such as the fullerene–ferrocene dyads of Yamamoto
et al.34 (Scheme 3). One of these (III) is structurally related to
13, and therefore 13 offered an interesting comparator to these
results.
Theoretical considerations
To support the experimental findings and to verify the electron
distribution within Fc-ethynyl-HBC (13), calculations were per-
formed (Gaussian 09,32 using the MO6 Hybrid functional33 and
6-31G(d,p) basis set) on the component fragments (Fe, Cp,
ethyne, and hexabenzocorenene (HBC)) in ferrocene, ethynyl-
The nonlinear response of 13 was studied by hyper Rayleigh
scattering (HRS)35–37 at λ = 1.9 μm for comparison with those
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Experimental
Tetracyclone (Aldrich), ferrocene (Aldrich) and 3,-5-dimethoxy-
benzyl bromide 3 (Aldrich) were used as received. Ethynyl-
ferrocene38 and dipyrimidyl acetylene39 and the uncyclised
iodo-polyphenylene precursor20 were synthesised according to lit-
erature procedures. Flash chromatography was performed using
silica gel (Brockman I, Aldrich Chemical) as the stationary phase.
Preparative thin layer chromatography was performed using silica
gel (1000 μm thickness) preparative thin layer chromatographic
plates (Aldrich). NMR spectra were recorded in CDCl3 using a
Bruker Avance DPX-400 MHz spectrometer (operating at
Scheme 3 Three fullerene–ferrocene dyads synthesised by Yamamoto
et al.34
Table 3 NLO response for compound 13, III, trans-(IV) and cis-(IV)
Complex
λ0/νμ
βa/10−30 esu
1
400.1 MHz for H, 100.6 MHz for 13C) or where stated using a
Bruker AV-600 MHz spectrometer (600.1 MHz for 1H,
13
(III)
trans-(IV)
cis-(IV)
396
328
329
324
260a
173b
568b
374b
1
150.6 MHz for 13C). H and 13C NMR spectra were referenced
relative to TMS (δ 0.00 ppm). Chemical shifts (δ) are reported in
ppm and coupling constants in Hertz. IR spectra (reported in
cm−1) were made as neat samples and were recorded on a Perkin-
Elmer Spectrum-One FT-IR spectrometer equipped with a Univer-
sal-ATR sampling accessory. Elemental analyses were performed
in the Microanalytical Laboratory, University College Dublin. As
is common for systems incorporating thermally robust polyaro-
matic frameworks, meaningful consistent elemental analysis
results were difficult to obtain for compound 13 due to incomplete
a Measured in chloroform by the HRS method at 1.910 μm. b Measured
in chloroform by the HRS method at 1.064 μm.
of (III), trans-(IV) and cis-(IV). As the UV-visible spectrum of
13 is complex, displaying several absorption bands, it was not
appropriate to use a two-level dispersion model to infer a β(0)
that would be independent of the fundamental wavelength λ.
From the data presented in Table 3 it is apparent that the β value
for 13 (260 × 10−30 esu at λ = 1.91 μm) at a low resonance
regime is higher than that of (III) (173 × 10−30 esu at λ =
1.06 μm) at a much more resonant regime. The direction and
magnitude of this difference (a factor of 1.5) is particularly sig-
nificant as all reported data on molecular NLO demonstrate an
increase in β when the fundamental wavelength comes close to
the absorption maxima (i.e. in a more resonant regime) even in
rather complex spectra. The improvement in the β value also
exceeds by far the experimental error of HRS measurements
(10% in our case) and thus the increase in hyperpolarizability
can be attributed to the greater electron-accepting character of
the ethynyl-HBC relative to ethynyl-fullerene. Molecules with
yet higher conjugation lengths such as that present in trans-(IV)
serve to maximise the NLO response further and to suggest
structural features that would constitute desirable additions to
future synthetic targets.
1
combustion of the fused all-carbon core. In the alternative, a H
NMR spectrum (Fig. 3) and the experimental (+)-MALDI-TOF
spectra and (MH)+ simulated isotopic distribution pattern for this
compound (Supporting Information,† Fig. S1) are provided. Elec-
trospray mass spectra were recorded on a Micromass-LCT spec-
trometer and accurate mass spectra were referenced against leucine
enkephalin ([M + H]+ m/z 556.2771 g mol−1) and reported to
within 5 ppm. MALDI-TOF mass spectra were recorded on a
Waters MALDI-QTOF premier spectrometer using an α-cyano-
4-hydroxy cinnamic acid matrix and accurate mass spectra were
referenced against [Glu1]-fibrinopeptide B ([M + H]+ m/z
1570.6768 g mol−1) and reported to within 5 ppm. Cyclic voltam-
metry was performed using a CH Instruments Electrochemical
Analyser Model 600B. Cyclic voltammograms were measured on
1 mM solutions using tetra-n-butylammonium hexafluorophos-
phate (TBAPF6, 0.1 M) as supporting electrolyte. A standard
three electrode cell was employed with a glassy carbon working
electrode, a Pt wire counter electrode and a SCE as the reference
electrode. Potentials are quoted versus the ferrocene–ferrocenium
couple (0.0 V) and all potentials were referenced to internal ferro-
cene added at the end of each experiment. Solutions were
degassed for several minutes by nitrogen bubbling before and
during the experiment. UV-Vis absorption spectra were recorded
as optically dilute solutions (10−4 − 5 × 10−7 M) in 1 × 1 cm2
quartz cuvettes on a Shimadzu UV-2450 spectrophotometer.
Conclusions
A number of synthetically useful ferrocenyl substituted di-
ketones, monoketones and acetylenes have been prepared as
building blocks in the formation of polyphenylenes that com-
prise up to four ferrocenyl units. Oxidative cyclodehydrogena-
tion via FeCl3-catalysed oxidation was not successful; however
hexa-peri-hexabenzocoronene (HBC) ethynyl ferrocene (13), a mole-
cular form of organometallic graphene was prepared via Sono-
gashira coupling using iodo-HBC. The UV-visible absorption
spectra, electrochemical and NLO data of this compound,
confirm electron donation from the Fe to the highly delocalised
Cp-ethynyl HBC unit. 13 is a novel conjugated organometallic
graphene which warrants further solid-state investigation and
synthetic derivatisation.
Compound 1
Ferrocene (7.6 g, 40.8 mmol) was added to sulfuric acid (50 mL,
spec. grav. 1.84) and the resulting deep blue ferrocenium solu-
tion was stirred at room temperature for 2 h. The solution was
then poured into ice/water (200 mL) and allowed to warm to
room temperature.
A solution of sodium nitrite (1.82 g, 13.2 mmol) in water
(10 mL) at 0 °C was added dropwise to a stirred solution of
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4-aminobenzylalcohol (3.0 g, 24 mmol) in 1 : 1 water/hydro-
chloric acid (spec. grav. 1.18) (20 mL) at 0 °C, and stirred at this
temperature for 30 min to ensure full diazotization. Copper
powder (2.0 g) was added to the ferrocenium solution and the
diazonium solution was added dropwise with vigorous stirring.
After 24 h stirring at room temperature, effervescence due to
liberated nitrogen had ceased and ascorbic acid (10 g) was added
to the dark mixture to reduce any remaining ferrocenium to fer-
rocene. Dichloromethane (200 mL) was added and the organic
layer separated. The aqueous layer was extracted further with
dichloromethane (4 × 100 mL), and the combined organic
extracts were filtered through celite before removal of the solvent
in vacuo to give a dark brown solid. This was subjected to
column chromatography using gradient elution. The first yellow
fraction, eluted with hexane, yielded ferrocene. The second
orange-red fraction was eluted with dichloromethane and 5%
methanol to give the desired product on removal of the solvents
in vacuo as an orange solid (2.2 g, 31%). mpt: 109–110 °C.
dichloromethane–water (180 mL). Argon was bubbled through
the mixture for 30 min to degas the solution. Compound 2
(5.5 g, 15.5 mmol) and iron pentacarbonyl (1.1 mL, 7.75 mmol)
were added to the reaction which was stirred at room temperature
for six hours under a constant stream of argon. The reaction
mixture was then oxidised in air and acidified with 10% HCl
(120 mL). The aqueous phase was extracted with dichloro-
methane and the organic washings were combined and their
volume reduced under vacuum. Column chromatography on
silica yielded the product as an orange solid after the removal of
solvent in vacuo (2.58 g, 58%). mpt: >200 °C (decomp.).
3
1H NMR (CDCl3, 20 °C) δ: 7.45 (d, 4H, JHH = 8.0 Hz, –CH
3
3
Ar), 7.11 (d, 4H, JHH = 8.0 Hz, –CH Ar), 4.65 (t, 4H, JHH
=
3
2.0 Hz, –CH Fc), 4.34 (s, 4H, JHH = 2.0 Hz, –CH Fc), 4.07 (s,
10H, –CH Fc), 3.75 (s, 4H, –CH2). 13C {1H} NMR (CDCl3,
20 °C): δ 205.47 (1C, –CO), 137.66 (2C, quat Ar), 131.02 (2C,
quat Ar), 129.07 (4C, –CH Ar), 125.98 (4C, –CH Ar), 84.60
(2C, quat Fc), 69.18 (10C, –CH Fc), 68.49 (4C, –CH Fc), 66.05
(4C, –CH Fc), 48.41 (2C, –CH2). ESI-MS (toluene) for
C35H30Fe2ONa: [M + Na]+ calculated m/z 601.0893, found m/z
601.0919. IR νbar (cm−1): ν(C–H st, aromatic): 3092, 3031,
ν(CvO st): 1722, ν(CvC st): 1612, 1603, 1527, ν(C–H rock
Fc): 1103, 1083, 1056, 999. Anal. Calcd for C35H30Fe2O·12H2O:
C, 71.58; H, 5.32. Found: C, 71.82; H, 5.16.
3
1H NMR (CDCl3, 20 °C): δ 7.50 (d, 2H, JHH = 8.3 Hz, –CH
Ar), 7.31 (d, 2H, 3JHH = 8.3 Hz, –CH Ar), 4.69 (s, 2H, –CH2–),
4.67 (t, 2H, 3JHH = 2.0 Hz, –CH Fc), 4.34 (t, 2H, 3JHH = 2.0 Hz,
–CH Fc), 4.07 (s, 5H, –CH Fc), 1.73 (br s, 1H, –OH). 13C {1H}
NMR (CDCl3, 20 °C): δ 138.34 (1C, quat Ar), 137.94 (1C,
quat Ar), 126.78 (2C, –CH Ar), 125.82 (2C, –CH Ar), 84.60
(1C, quat Fc), 69.17 (5C, –CH Fc), 68.52 (2C, –CH Fc), 66.06
(2C, –CH Fc), 64.83 (1C, –CH2). ESI-MS (toluene) for
C17H16FeO: [M]+ calculated m/z 292.0551, found m/z 292.0552.
Anal. Calcd for C17H16FeO·CH2Cl2: C, 57.33; H, 4.81. Found:
C, 57.41; H, 4.87.
Compound 5
Calcium hydroxide (3.2 g, 43.2 mmol) and tetrabutylammonium
hydrogensulfate (1.83 g, 5.7 mmol) were dissolved in 1 : 1
dichloromethane–water (240 mL) and argon was bubbled
through the reaction mixture for 30 min to degas the solution.
3,5-Dimethoxybenzyl bromide (3) (5.0 g, 21.6 mmol) was
added followed by iron pentacarbonyl (1.5 mL, 10.8 mmol) and
the reaction was stirred at room temperature for five and a half
hours under a constant stream of argon. The reaction mixture
was then oxidised in air and acidified with 10% HCl (120 mL).
The aqueous phase was extracted with dichloromethane and the
organic washings were combined and the volume reduced
in vacuo to give a yellow/orange oil. The oil was subjected to
column chromatography on silica. Eluting with diethyl ether
yielded the desired product as an off-white waxy solid (2.3 g,
Compound 2
Compound 1 (1 g, 3.42 mmol) was dissolved in dichloro-
methane (20 mL) in a 3-necked round bottomed flask. The
mixture was cooled to 0 °C, and a solution of phosphorous tri-
bromide (0.7 mL, 1.85 g, 6.85 mmol) dissolved in dichloro-
methane (5 mL) was added dropwise. The resulting mixture was
then stirred at 0 °C for 30 min. The reaction mixture was poured
onto ice (100 g), neutralised with saturated aqueous sodium
hydrogen carbonate solution and the organic phase separated.
The aqueous phase was extracted with dichloromethane, and the
organic phases were collected. These were washed with brine
and dried over MgSO4 to yield the product as an orange powder
on the removal of the solvent in vacuo (1.14 g, 94%). mpt:
1
65%). mpt: 78–80 °C. H NMR (CDCl3, 20 °C): δ 6.39 (t, 2H,
4
4JHH = 2.0 Hz, –CH Ar), 6.32 (d, 4H, JHH = 2.0Hz, –CH Ar),
3.78 (s, 12H, –OCH3), 3.66 (s, 4H, –CH2–). 13C {1H} NMR
(CDCl3, 20 °C): δ 205.04 (1C, –CO), 160.51 (4C, quat Ar),
135.64 (2C, quat Ar), 107.07 (4C, –CH Ar), 98.71 (2C,
–CH Ar), 54.86 (2C, –CH2–), 48.78 (4C, –OCH3). ESI-MS
1
>200 °C (decomp.). H NMR (CDCl3, 20 °C): δ 7.47 (d, 2H,
3
3JHH = 8.5 Hz, –CH Ar), 7.33 (d, 2H, JHH = 8.5 Hz, –CH Ar),
3
6.67 (t, 2H, JHH = 2.0Hz, –CH Fc), 4.54 (s, 2H, –CH2–), 4.36
(s, 2H, 3JHH = 2.0 Hz, –CH Fc), 4.08 (s, 5H, –CH Fc). 13C {1H}
NMR (CDCl3, 20 °C) δ: 139.46 (1C, quat Ar), 134.67 (1C, quat
Ar), 128.69 (2C, –CH Ar), 125.97 (2C, –CH Ar), 84.13 (1C,
quat Fc), 69.23 (5C, –CH Fc), 68.73 (2C, –CH Fc), 66.17 (2C,
–CH Fc), 33.52 (1C, –CH2). Anal. Calcd for C17H15BrFe: C,
57.51; H, 4.26. Found: C, 58.06; H, 4.42.
(methanol) for C19H22O5Na: [M +
Na]+ calculated m/z
353.1365, found m/z 353.1374. Anal. Calcd for C19H22O5: C,
69.07; H, 6.71. Found: C, 69.34; H, 6.84.
Compound 6
4-Ferrocenylbenzoaldehyde (2 g, 6.89 mmol) and sodium
cyanide (0.6 g, 12.2 mmol) were dissolved in water (3 mL) and
ethanol (10 mL) and refluxed for 1 h. The solution was cooled,
resulting in a red precipitate, which was collected by suction
filtration. The precipitate was dried and subjected to column
Compound 4
Calcium hydroxide (2.3 g, 31 mmol) and tetrabutylammonium
hydrogensulfate (1.32 g, 3.88 mmol) were dissolved in 1 : 1
8856 | Dalton Trans., 2012, 41, 8850–8860
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3
chromatography on silica eluting with dichloromethane. The first
orange band yielded unreacted 4-ferrocenylbenzaldehyde and the
second orange-red band afforded the desired product as an
orange crystalline solid on recrystallisation from hexane (1.18 g,
59%). mpt: 117–118 °C. 1H NMR (CDCl3, 20 °C): δ 7.87
3JHH = 8.0 Hz, –CH Ar), 7.30 (d, 4H, JHH = 8.0 Hz, –CH Ar),
3
3
6.94 (d, 4H, JHH = 8.5 Hz, –CH Ar), 4.67 (t, 4H, JHH
2.0 Hz, –CH Fc), 4.64 (t, 4H, JHH = 2.0 Hz, –CH Fc), 4.35 (t,
=
3
3
3
4H, JHH = 2.0 Hz, –CH Fc), 4.33 (t, 4H, JHH = 2.0 Hz,
–CH Fc), 4.05 (s, 10H, –CH Fc), 4.04 (s, 10H, –CH Fc). 13C
{1H} NMR (150.6 MHz) (CDCl3, 20 °C): δ 200.74 (1C, –CO),
153.79 (2C, quat Ar), 139.94 (2C, quat Ar), 138.38 (2C, quat
Ar), 130.76 (2C, quat Ar), 129.92 (4C, –CH Ar), 129.51 (4C,
–CH Ar), 128.50 (2C, quat Ar), 125.53 (4C, –CH Ar), 124.95
(4C, –CH Ar), 124.49 (2C, quat Ar), 84.78 (2C, quat Fc), 83.70
(2C, quat Fc), 69.75 (10C, –CH Fc), 69.51 (10C, –CH Fc),
69.36 (4C, –CH Fc), 68.93 (4C, –CH Fc)), 66.32 (4C, –CH Fc),
66.25 (4C, –CH Fc). MALDI-TOF MS (methanol) for
C69H52Fe4O: [M]+ calculated m/z 1120.1416, found m/z
1120.1416. IR νbar (cm−1): ν(C–H st, aromatic): 3076, ν(CvO
st): 1706, ν(CvC st): 1600, 1526, 1517, ν(C–H rock Fc): 1103,
1088, 1082, 1017. Note: Instability of solid precluded C, H, N
analysis.
3
(d, 2H, JHH = 8.5 Hz, –CH Ar), 7.47,(m, 4H, –CH Ar), 7.30
3
3
(d, 2H, JHH = 8.5 Hz, –CH Ar), 5.91 (d, 1H, JHH = 6.0 Hz,
–CH(OH)), 4.68 (s, 2H, –CH Fc), 4.63 (s, 2H, –CH Fc), 4.55 (d,
3
1H, JHH = 6.0 Hz, –OH), 4.41 (s, 2H, –CH Fc), 4.32 (s, 2H,
–CH Fc), 4.02 (s, 10H, –CH Fc). 13C {1H} NMR (CDCl3,
20 °C): δ 197.63 (1C, –CO), 146.39 (1C, quat Ar), 139.41 (1C,
quat Ar), 136.52 (1C, quat Ar), 130.19 (1C, quat Ar), 128.84
(2C, –CH Ar), 127.30 (2C, –CH Ar), 126.19 (2C, –CH Ar),
125.31 (2C, –CH Ar), 83.95 (1C, quat Fc), 82.17 (1C, quat Fc),
75.25 (1C, –CH(OH)), 69.39 (5C, –CH Fc), 69.14 (5C, –CH
Fc), 66.66 (2C, –CH Fc), 66.46 (2C, –CH Fc), 66.09 (2C, –CH
Fc), 66.06 (2C, –CH Fc). ESI-MS (methanol) for C34H28Fe2O2:
[M]+ calculated m/z 580.0788, found m/z 580.0773. IR νbar
(cm−1): ν(O–H st): 3444, ν(C–H st, aromatic): 3095, 2960,
ν(CvO st): 1665, ν(CvC st): 1601, 1561, 1526, ν(C–H rock
Fc): 1106, 1069, 1031. Anal. Calcd for C34H28Fe2O2: C, 70.37;
H, 4.86. Found: C, 70.42; H, 5.00.
Compound 9
Diketone 7 (1.3 g, 2.25 mmol) and potassium hydroxide (0.22 g,
3.85 mmol) were dissolved in ethanol (25 mL) and heated to
reflux. A solution of 5 (0.79 g, 2.4 mmol) was dissolved in
ethanol (25 mL) and added dropwise to the reaction mixture
which was refluxed for 3 h. The solution was then cooled slowly
to room temperature and the dark green crystalline product was
isolated by filtration (0.38 g, 64%). mpt: 204–205 °C. H NMR
(CDCl3, 20 °C): δ 7.32 (d, 4H, JHH = 8.5 Hz, –CH Ar), 6.91
(d, 4H, JHH = 8.5 Hz, –CH Ar), 6.51 (d, 4H, JHH = 2.0 Hz,
Compound 7
(Reaction carried out in air.) Compound 6 (1.2 g, 2.07 mmol)
was dissolved in chloroform (30 mL). Manganese dioxide
(0.72 g, 8.27 mmol) was added and the mixture was refluxed for
24 h. After cooling to room temperature, the solution was filtered
through celite and the filtrant was washed until the filtrate ran
clear. The solvent was removed in vacuo yielding the desired
product as an orange-red solid (1.05 g, 88%). mpt: 134–135 °C.
1
3
3
4
4
–CH Ar), 6.39 (t, 2H, JHH = 2.0 Hz, –CH Ar), 4.64 (t, 4H,
3
3JHH = 1.8 Hz, –CH Fc), 4.34 (t, 4H, JHH = 1.8 Hz, –CH Fc),
1H NMR (CDCl3, 20 °C): δ 7.93 (d, 4H, JHH = 8.5 Hz, –CH
4.01 (s, 10H, –CH Fc), 3.66 (s, 12H, –OCH3). 13C {1H} NMR
(CDCl3, 20 °C) δ: 199.36 (1C, –CO), 159.81 (4C, quat Ar),
154.30 (2C, quat Ar), 139.78 (2C, quat Ar), 132.17 (2C, quat
Ar), 129.98 (2C, quat Ar), 129.16 (4C, –CH Ar), 124.68 (4C,
–CH Ar), 124.26 (2C, quat Ar), 107.47 (4C, –CH Ar), 100.11
(2C, –CH Ar), 83.40 (2C, quat Fc), 69.37 (10C, –CH Fc), 69.04
(4C, –CH Fc), 65.96 (4C, –CH Fc), 54.71 (4C, –OCH3).
ESI-MS (toluene) for C53H44Fe2O5: [M]+ calculated m/z
872.1888, found m/z 872.1897. IR νbar (cm−1): ν(C–H st, aro-
matic): 3086, 2997, ν(C–H st, –OCH3): 2834, ν(CvO st): 1702,
ν(CvC st): 1603, 1589, 1524, ν(C–O st, –OCH3): 1275, ν(C–H
rock Fc): 1193, 1104, 1096, 1044. Anal. Calcd for C53H44Fe2O5:
C, 72.95; H, 5.08. Found: C, 72.71; H, 4.89.
3
3
3
Ar), 7.57 (d, 4H, JHH = 8.5 Hz, –CH Ar), 4.77 (t, 4H, JHH
=
3
1.5 Hz, –CH Fc), 4.47 (t, 4H, JHH = 1.5 Hz, –CH Fc), 4.07 (s,
10H, –CH Fc). 13C {1H} NMR (CDCl3, 20 °C): δ 193.71 (2C,
–CO), 147.54 (2C, quat Ar), 129.95 (2C, quat Ar), 129.75 (4C,
–CH Ar), 125.61 (4C, –CH Ar), 82.38 (2C, quat Fc), 70.14 (4C,
–CH Fc), 69.78 (10C, –CH Fc), 66.89 (4C, –CH Fc). ESI-MS
(methanol) for C34H26Fe2O2Na: [MNa]+ calculated m/z
601.0529, found m/z 601.0532. IR νbar (cm−1): ν(C–H st, aro-
matic): 3096, 2961, ν(CvO, st): 1670, 1658, ν(CvC st): 1604,
1560, 1523, ν(C–H rock Fc): 1218, 1173, 1103, 1082. Anal.
Calcd for C34H26Fe2O2·H2O: C, 68.49; H, 4.73. Found: C,
68.61; H, 4.73.
Compound 8
Compound 10
Diketone 7 (0.5 g, 0.86 mmol) and potassium hydroxide (0.08 g,
1.47 mmol) were dissolved in ethanol (25 mL) and heated to
reflux. A solution of 4 (0.55 g, 0.95 mmol) dissolved in
ethanol–dichloromethane, 1 : 1 (45 mL) and added dropwise to
the mixture which was then refluxed for 18 h. The solution was
cooled to room temperature, and the resulting precipitate
was filtered and washed with ethanol followed by hexane to
yield the desired product as an unstable purple solid (0.61 g,
Cyclopentadienone 8 (0.25 g, 0.22 mmol), di(5-pyrimidyl)acety-
lene (0.037 g, 0.2 mmol) and benzophenone (1.0 g) were mixed
in a round bottomed flask and attached to an air condenser. The
mixture was heated at 200 °C for 18 h. The mixture was then
subjected to flash column chromatography on silica. Eluting
with dichloromethane removed all the benzophenone and any
un-reacted cyclopentadienone. Elution with diethyl ether–metha-
nol (10 : 1) and removal of the solvents yielded the desired
product as a light orange powder (0.14 g, 54%). mpt: >200 °C
1
63%). mpt: <100 °C (decomp.). H NMR (600.1 MHz) (CDCl3,
3
1
20 °C): δ 7.39 (d, 4H, JHH = 8.5 Hz, –CH Ar), 7.34 (d, 4H,
(decomp.). H NMR (600.1 MHz) (CDCl3, 20 °C): δ 8.81 (s,
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3
2H, –CH Ar), 8.32 (s, 4H, –CH Ar), 7.12 (d, 4H, JH1H = 8.0
with dichloromethane followed by recrystallisation from hexane
yielded the desired product as an orange-red powder (0.07 g,
18%). mpt: >200 °C (decomp.). 1H NMR (C2D2Cl4, 60 °C):
Hz, –CH Ar), 7.07 (d, 4H, 3JHH = 8.0 Hz, –CH Ar), 6.81 (d, 4H,
3JHH = 8.0 Hz, –CH Ar), 6.78 (d, 4H, JHH = 8.0 Hz, –CH Ar),
3
3
3
4.53 (s, 4H, –CH Fc), 4.48 (s, 4H, –CH Fc), 4.26 (s, 4H, –CH
Fc), 4.21 (s, 4H, –CH Fc), 3.92 (s, 10H, –CH Fc), 3.91 (s, 10H,
–CH Fc). 13C {1H} NMR (150.6 MHz) (CDCl3, 20 °C) δ:
157.98 (4C, –CH Ar), 156.05 (2C, –CH Ar), 142.42 (2C, quat
Ar), 141.48 (2C, quat Ar), 137.48 (2C, quat Ar), 136.85 (2C,
quat Ar), 136.68 (2C, quat Ar), 136.04 (2C, quat Ar), 133.90
(2C, quat Ar), 133.06 (2C, quat Ar), 131.18 (4C, –CH Ar),
131.08 (4C, –CH Ar), 124.68 (4C, –CH Ar), 124.21 (4C, –CH
Ar), 84.23 (2C, quat Fc), 83.61 (2C, quat Fc), 69.74 (10C, –CH
Fc), 69.69 (10C, –CH Fc), 69.00 (4C, –CH Fc), 66.12 (4C, –CH
Fc), 66.02 (4C, –CH Fc), 60.05 (4C, –CH Fc). MALDI-TOF
MS for C78H58Fe4N4: [M]+ calculated m/z 1274.2059, found m/z
1274.2003. IR νbar (cm−1): ν(C–H st, aromatic): 3093, 3024,
ν(CvC st): 1608, ν(CvN st): 1548, 1529, ν(C–H rock Fc):
1104, 1082, 1049, 1019. Anal. Calcd for C78H58Fe4N4·12CH3OH:
C, 73.20; H, 4.65; N, 4.36. Found: C, 73.17; H, 4.67; N, 4.40.
δ 7.06 (d, 8H, JHH = 8.0 Hz, –CH Ar), 6.83 (d, 8H, JHH =
4
8.0 Hz, –CH Ar), 6.14 (d, 4H, JHH = 2.0 Hz, –CH Ar), 6.02 (t,
2H, 4JHH = 2.0 Hz, –CH Ar), 4.54 (s, 8H, –CH Fc), 4.23 (s, 8H,
–CH Fc), 3.91 (s, 20H, –CH Fc), 3.48 (s, 12H, –OCH3).
13C {1H} NMR (150.6 MHz) (CDCl3, 20 °C) δ: 159.23 (4C,
quat Ar), 142.42 (2C, quat Ar), 140.13 (2C, quat Ar), 139.91
(4C, quat Ar), 138.44 (2C, quat Ar), 136.06 (4C, quat Ar),
130.97 (8C, –CH Ar), 123.89 (8C, –CH Ar), 110.09 (4C, –CH
Ar), 97.57 (2C, –CH Ar), 70.17 (8C, –CH Fc), 69.30 (4C, quat
Fc), 66.19 (8C, –CH Fc), 54.87 (24C, –CH Fc & –OCH3).
MALDI-TOF MS for C86H70Fe4O4: [M]+ calculated m/z
1390.2672, found m/z 1390.2739. IR νbar (cm−1): ν(C–H st, aro-
matic): 3088, 3020, ν(C–H st, –OCH3): 2952, 2833, ν(CvC st):
1606, 1562, 1529, ν(C–O st, –OCH3): 1274, ν(C–H rock Fc):
1158, 1104, 1062. Anal. Calcd for C86H70Fe4O4: C, 74.27; H,
5.07. Found: C, 74.04; H, 4.83.
Compound 11
Iodo-HBC
Cyclopentadienone 9 (0.4 g, 0.46 mmol), dipyrimidyl acetylene
(0.075 g, 0.41 mmol) and benzophenone (1.5 g) were mixed in a
round bottomed flask and attached to an air condenser. The
mixture was heated at 200 °C for 18 h. The mixture was then
subjected to flash column chromatography on silica. Eluting
with dichloromethane removed all the benzophenone and any
un-reacted cyclopentadienone. Elution with diethyl ether–metha-
nol (9 : 1) and removal of the solvents in vacuo yielded the
desired product as an orange powder (0.24 g, 58%). mpt:
A solution of iron(III) chloride (1.8 g, 14.0 mmol) in nitro-
methane (3 mL) was added dropwise to a stirred solution of the
uncyclised iodo-polyphenylene precursor (0.35 g, 0.47 mmol) in
dichloromethane (40 mL). An argon stream was bubbled through
the reaction mixture throughout the entire reaction. After stirring
for 45 min the reaction was quenched with methanol (40 mL).
The precipitate was filtered, washed with methanol (100 mL)
and dried under reduced pressure. The crude product was
purified by column chromatography on silica, elution with
hexane–dichloromethane (4 : 1) and removal of the solvents
yielded the desired product as an off-white crystalline solid
1
>200 °C (decomp.). H NMR (CDCl3, 20 °C): δ 8.86 (s, 2H,
3
–CH Ar), 8.33 (s, 4H, –CH Ar), 7.05 (d, 4H, JHH = 8.0 Hz,
3
1
–CH Ar), 6.80 (d, 4H, JHH = 8.0 Hz, –CH Ar), 6.05 (m, 6H,
(0.30 g, 85%). mpt: >300 °C. H NMR (CDCl3, 20 °C) δ: 9.20
–CH Ar), 4.55 (s, 4H, –CH Fc), 4.26 (s, 4H, –CH Fc), 3.89 (s,
10H, –CH Fc), 3.52 (s, 12H, –OCH3). 13C {1H} NMR
(600 MHz) (CDCl3, 20 °C): δ 159.87 (4C, quat Ar), 157.68 (4C,
–CH Ar), 156.09 (2C, quat Ar), 142.40 (2C, quat Ar), 141.34
(2C, quat Ar), 140.21 (2C, quat Ar), 136.77 (2C, quat Ar),
136.68 (2C, quat Ar), 133.73 (2C, quat Ar), 132.62 (2C, –CH
Ar), 130.57 (4C, –CH Ar), 124.15 (4C, –CH Ar), 109.85 (4C,
–CH Ar), 98.51 (2C, –CH Ar), 84.36 (2C, quat Fc), 69.81 (10C,
–CH Fc), 69.12 (4C, –CH Fc), 66.05 (4C, –CH Fc), 55.03 (4C,
–OCH3). MALDI-TOF MS; for C62H50Fe2N4O4: [M]+ calcu-
lated m/z 1026.2531, found m/z 1026.2560. IR νbar (cm−1):
ν(C–H st, aromatic): 3024, 2939, ν(C–H st, –OCH3): 2837,
ν(CvC st): 1607, ν(CvN st): 1603, 1550, ν(C–O st, –OCH3):
1279, ν(C–H rock Fc): 1200, 1161, 1136. Anal. Calcd for
C62H50Fe2N4O4: C, 72.52; H, 4.91; N, 5.46. Found: C, 72.70;
H, 4.71; N, 5.24.
(s, 2H, –CH Ar), 9.15 (s, 2H, –CH Ar), 9.07 (s, 2H, –CH Ar),
8.96 (s, 2H, –CH Ar), 8.86 (s, 2H, –CH Ar), 8.69 (s, 2H, –CH
Ar), 1.95 (s, 9H, –C(CH3)3), 1.91 (s, 18H, –C(CH3)3), 1.82
(s, 18H, –C(CH3)3). 13C {1H} NMR (CDCl3, 20 °C): δ 148.56
(quat Ar), 148.40 (quat Ar), 148.37 (quat Ar), 131.97 (quat Ar),
130.17 (quat Ar), 129.92 (quat Ar), 129.84 (quat Ar), 129.68
(quat Ar), 129.61 (2C, –CH Ar), 128.23 (quat Ar), 124.06 (quat
Ar), 123.25 (quat Ar), 123.21 (quat Ar), 123.09 (quat Ar),
120.22 (quat Ar), 119.83 (quat Ar), 119.72 (quat Ar), 118.95
(quat Ar), 118.88 (2C, –CH Ar), 118.85 (2C, –CH Ar), 118.58
(2C, –CH Ar), 118.54 (2C, –CH Ar), 118.48 (2C, –CH Ar),
35.65 (1C, quat –C(CH3)3), 35.59 (2C, quat –C(CH3)3), 35.52
(2C, quat –C(CH3)3), 32.01 (3C, –CH, –C(CH3)3), 31.98 (6C,
–CH, –C(CH3)3), 31.93 (6C, –CH, –C(CH3)3). MALDI-TOF
MS calculated for C62H57I: [M]+ calculated m/z 928.3505, found
m/z 928.3549. IR νbar (cm−1): ν(C–H st, aromatic): 3099,
ν(C–H st, –CH3): 2953, 2902, 2866. Anal. Calcd for C62H57I:
C, 80.16; H, 6.18. Found: C, 79.92; H, 6.03.
Compound 12
1,2-Bis(p-ferrocenylphenyl)acetylene (0.15 g, 0.27 mmol), 9
(0.30 g, 0.34 mmol) and benzophenone (2 g) were mixed in a
round bottomed flask and attached to an air condenser. The
mixture was heated at 190 °C for 24 h. The mixture was then
subjected to flash column chromatography on silica. Eluting
Compound 13
Ethynylferrocene (0.027 g, 0.13 mmol) was dissolved in triethyl-
amine (3 mL) and added via cannula to a solution of iodo-HBC
(0.1 g, 0.11 mmol) and tetrakis(triphenylphosphino)palladium
8858 | Dalton Trans., 2012, 41, 8850–8860
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(0.006 g, 0.006 mmol) in toluene (8 mL). The mixture was
heated at 70 °C for 18 h. The solvents were removed in vacuo,
washed with water and extracted into dichloromethane. The
organic phase was dried over MgSO4, solvents removed
in vacuo again before being subjected to column chromato-
graphy on silica. Elution with hexane–dichloromethane (1 : 1)
followed by recrystallisation from methanol yielded the desired
product as a fine orange-red powder (0.08 g, 77%). mpt:
>200 °C (decomp.). 1H NMR (600.1 MHz) (CDCl3, 20 °C):
δ 9.24 (s, 2H, –CH Ar), 9.18 (s, 2H, –CH Ar), 9.13 (s, 2H, –CH
Ar), 9.04 (s, 2H, –CH Ar), 8.91 (s, 2H, –CH Ar), 8.81 (s, 2H,
–CH Ar), 4.85 (s, 2H, –CH Fc), 4.50 (s, 5H, –CH Fc), 4.46 (s,
2H, –CH Fc), 1.98 (s, 9H, –C(CH3)3), 1.95 (s, 18H, –C(CH3)3),
1.89 (s, 18H, –C(CH3)3). 13C {1H} NMR (150.6 MHz) (CDCl3,
20 °C): δ 148.72 (quat Ar), 148.69 (quat Ar), 148.61 (quat Ar),
130.49 (quat Ar), 130.31 (quat Ar), 130.14 (quat Ar), 130.10
(quat Ar), 129.98 (quat Ar), 129.28 (quat Ar), 124.80 (quat Ar),
124.21 (2C, –CH Ar), 123.52 (quat Ar), 123.49 (quat Ar),
123.47 (quat Ar), 121.46 (quat Ar), 120.47 (quat Ar), 120.30
(quat Ar), 120.12 (quat Ar), 119.59 (quat Ar), 119.32 (2C, –CH
Ar), 118.99 (2C, –CH Ar), 118.83 (2C, –CH Ar), 118.80 (2C,
–CH Ar), 118.78 (2C, –CH Ar), 91.50 (1C, quat Fc), 89.21 (1C,
–CuC–), 87.39 (1C, –CuC–), 71.51 (2C, –CH Fc), 69.98 (5C,
–CH Fc), 68.93 (2C, –CH Fc), 35.62 (3C, quat, –C(CH3)3),
35.59 (2C, quat, –C(CH3)3), 31.98 (6C, –CH, –C(CH3)3), 31.94
(9C, –CH, –C(CH3)3). MALDI-TOF MS for C74H66Fe: [M]+
calculated m/z 1010.4514, found m/z 1010.4509. IR ν (cm−1):
ν(C–H st, aromatic): 3099, ν(C–H st, –CH3): 2954, 2904, 2666,
ν(CuC st): 2200 ν(CvC st): 1606, 1578, ν(C–H rock Fc):
1090, 1055.
processed by a computer. The reference beam is collected at a
45° incidence angle by a glass plate and focused onto a highly
nonlinear NPP (N-4-nitrophenyl-prolinol) powder used as a fre-
quency doubler. The variation of the scattered second harmonic
intensity from the solution is recorded on the computer as a func-
tion of the reference second harmonic signal provided by the
NPP powder. β values are then inferred from the slopes of the
resulting lines. The relative experimental error for β values is
≤10%.
Acknowledgements
We thank Dr John O’Brien and Dr Martin Feeney for technical
assistance. The work was financially supported by Science Foun-
dation Ireland (05 PICA-I819, SFI-08RFPCHE1465 and STTF).
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8860 | Dalton Trans., 2012, 41, 8850–8860
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