Synthesis and spectroscopy of anthracene-containing linear and 'T'-shaped π-conjugated ligands

Article abstract of DOI:10.1016/j.jorganchem.2005.12.024

A range of new π-conjugated ethynyl- and diethynyl-benzene ligands has been synthesised and their spectroscopic characterisation carried out, most notably via IR and ¹H NMR. X-ray crystal structures were obtained for three of these ligands and

Full text of DOI:10.1016/j.jorganchem.2005.12.024

Journal of Organometallic Chemistry 691 (2006) 1389–1401
www.elsevier.com/locate/jorganchem
Synthesis and spectroscopy of anthracene-containing linear
and ‘T’-shaped p-conjugated ligands
*
Ian Cade, Nicholas J. Long , Andrew J.P. White, David J. Williams
Department of Chemistry, Imperial College London, Exhibition Road, South Kensington, London SW7 2AZ, United Kingdom
Received 11 November 2005; received in revised form 8 December 2005; accepted 8 December 2005
Available online 25 January 2006
Abstract
A range of new p-conjugated ethynyl- and diethynyl-benzene ligands has been synthesised and their spectroscopic characterisation car-
ried out, most notably via IR and 1H NMR. X-ray crystal structures were obtained for three of these ligands and one unusual ruthenium
complex. Both the 4-ethynyl- and 2,5-diethynyl-benzene cores of these compounds have been functionalised through organic transforma-
tions by addition of an 9-anthracenyl. This has been attached via a range of linker moieties that vary in both their length and degree of
p-conjugation. This has given rise to two groups of compounds with either a linear, e.g., 9-(2-(4-ethynylphenyl)ethynediyl)anthracene and
9-(2-(4-ethynylphenyl)ethyl)anthracene, or ‘T’-shaped morphologies, e.g., 9-(2-(2,5-diethylnylphenyl)ethyl)anthracene.
ꢀ 2005 Elsevier B.V. All rights reserved.
Keywords: Metal-alkynyl; p-Conjugated ligands
1. Introduction
This signalling ‘antenna’ moiety would take the form of a
group that may interact with the macroscopic world by,
for example, oxidation and reduction or by absorption of
light, changing the properties of the conductive framework.
With these considerations in mind, we report herein a
series of new p-conjugated ligands possessing a p-conju-
gated framework (the ethynyl benzene moieties) and an
antenna group (anthracene). These two components are
connected via a range of linkers that vary in their physical
length, flexibility and electronic properties. In addition,
trends in the spectroscopic data (1H NMR, IR) are also
analysed to obtain information about possible electronic
communication, and the formation of an unusual ruthe-
nium complex.
Considerable efforts have been made in preparing and
characterising p-conjugated organic molecules with rela-
tively high conductivities suitable as frameworks for future
molecular electronic applications [1–3]. However, molecu-
lar conductors are not the sole requirement for preparing
molecular analogues to modern electronic components.
For this, molecular analogues to the fundamental unit of
electronics, i.e. transistors, are required [4]. Such an ana-
logue would have to appear schematically the same as a
transistor, namely, possessing three terminals. One termi-
nal would allow a signal to be received by the molecular
transistor and translated into a modification of the proper-
ties of the molecule between the remaining two terminals.
The signal should be applied via an additional moiety
attached via a linker to the basic conductive framework,
as this would allow variation of the switching signal with
a minimised impact on the operation of the framework.
2. Results and discussion
2.1. Synthesis of linear ligands
In order to systematically examine the effects of an
anthracene moiety upon a nearby p-conjugated ethynylben-
zene ligand the two were covalently attached via a range of
linker groups. These linkers vary both in physical length
*
Corresponding author. Tel.: +44 020 75945781; fax: +44 020
75945804.
E-mail address: n.long@imperial.ac.uk (N.J. Long).
0022-328X/$ - see front matter ꢀ 2005 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2005.12.024

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I. Cade et al. / Journal of Organometallic Chemistry 691 (2006) 1389–1401
1-position doublet. The remaining protons, anthracene 2-
and 3-positions and the phenyl ring, give overlapping
signals.
The IR spectrum recorded from a DCM solution of A0L
showed both the terminal ethynyl carbon–proton and car-
bon–carbon stretches at 3296 and 2110 cmꢀ1, respectively.
Uniquely, within this series of compounds, A0L displayed
a second C„C stretch at 2196 cmꢀ1 due to the internal
ethynyl group. The marked difference between the stretch-
ing frequencies of the two carbon–carbon triple bonds is
due to a peculiarity associated with terminal acetylenes.
This involves the vibrations of the carbon–proton bond
coupling with those of the carbon–carbon bond, dispropor-
tionately lowering the apparent strength of the terminal tri-
ple bond [5].
A0L
A1L
A1T
A2T
A2L
A3T
A3L
2.3. Synthesis of A1L
Fig. 1. Compound structures and abbreviations used throughout the
following discussion: A, anthracene; 0–3, length of linker moiety; L,T,
linear or ‘T’-shaped geometry.
Compound A1L, 9-[2-(4-ethynyl-phenyl)-vinyl]-anthra-
cene, was prepared via a Wittig reaction, coupling the ylide
derived from a 9-anthracene methylphosphonium salt and
an ethynyl substituted benzaldehyde, to yield the desired
1
and degree of unsaturation, giving rise to a range of anthra-
cene-functionalised mono- and di-topic ligands, shown in
Fig. 1. The labelling is due to 9-anthracene (A), the spacing
unit may be either ethynyl, ethenyl, ethyl or propyl giving
rise to the ‘0’–‘3’ parts, respectively (the numbering starts
at ‘0’ to give the ethyl and propyl species the more intuitive
‘2’ and ‘3’ labels). The core benzene ring may be either 4- or
2,5-substituted resulting in the ethynyl groups being either
in line with, or as the crossbar of a ‘T’ to the antenna moiety
hence ‘L’ (linear) or ‘T’ abbreviations.
trans carbon–carbon double bond linker. H NMR spec-
troscopy showed two doublets at 7.95 and 6.94 ppm with
3
equal JH–H coupling constants of approximately 16 Hz
from the two ethenyl protons. Again this compound was
isolated as a bright yellow solid, which crystallised very
easily from a concentrated DCM solution. In contrast to
A0L, A1L exhibited a strong green fluorescence, which
was visibly weaker than that of A0L. In addition to the eth-
1
enyl proton signals, the H NMR spectrum of this ligand
also displayed the expected anthracene set of peaks
between 7.50 and 8.50 ppm along with a peak at
3.17 ppm associated with the terminal acetylene. The trans
geometry of the carbon linkages was confirmed by an X-
ray crystal structure. Compound A1L (Fig. 2) crystallises
with two independent molecules (A and B) in the asymmet-
ric unit. Their conformations are virtually identical, a best-
fit of the non-hydrogen atoms having a RMS deviation of
2.2. Synthesis of A0L
The synthesis of ligand A0L, 9-(4-ethynyl-phen-
ylethynediyl)-anthracene, was straightforward due to its
high symmetry. Thus, the ethynyl linker of A0L was pre-
pared by simply coupling a 1.1:1 mixture of commercially
available 1,4-diethynylbenzene and 9-bromoanthracene
using Sonogashira conditions. A small amount of the
expected disubstituted 1,4-di(2-(9-anthracenylethynediyl)-
benzene) was formed but this was typically a minor product
and the desired A0L could be obtained as a bright yellow
crystalline solid via column chromatography. Further puri-
fication was possible by recrystallising from a DCM/hexane
solution. This compound when in solution exhibited a
strong blue fluorescence under ambient laboratory illumi-
nation, visible to the naked eye, which allowed a qualitative
determination of the progress of the coupling reaction.
˚
only 0.14 A. The small differences in conformation are in
the torsional twists about the C(6)–C(9) and C(10)–C(11)
which are 3ꢁ and 51ꢁ in one molecule and 14ꢁ and 48ꢁ in
the other. As is observed in A3L (see later) there are no
p–p stacking interactions involving either the phenyl or
anthracene ring systems. There are, however, extensive
C–Hꢁ ꢁ ꢁp interactions between the two independent mole-
cules (Fig. 3).
2.4. Synthesis of A2L
1
The H NMR spectrum of A0L displayed the expected
Compound A2L, 9-[2-(4-ethynyl-phenyl)-ethyl]-anthra-
cene, was prepared via a Wittig reaction, as for A1L,
followed by reduction of the central ethenyl linker to the
ethyl analogue. This synthetic route required that the
terminal ethynyl group was added, via a Sonogashira cou-
pling of the aryl bromide with TMSA, following the reduc-
tion of the linker double bond (Fig. 4) rather than before
anthracene set of signals and those associated with the core
phenyl ring and terminal acetylene. A singlet at 3.22 ppm is
due to the terminal ethynyl proton, between 7.50 and
8.50 ppm are the aromatic resonances and working from
low field to high field they are due to the protons on
anthracene, i.e. a 4-position doublet, 10-position singlet,

I. Cade et al. / Journal of Organometallic Chemistry 691 (2006) 1389–1401
1391
˚
Fig. 2. One (A) of the pair of independent molecules in the structure of A1L. Selected bond lengths (A) and bond angles (ꢁ) [values for the second
independent molecule (B) in square parentheses]; C(6)–C(9) 1.476(5) [1.464(4)], C(9)–C(10) 1.307(4) [1.333(4)], C(10)–C(11) 1.477(5) [1.468(4)] and C(10)–
C(9)–C(6) 128.3(3) [127.8(3)], C(9)–C(10)–C(11) 124.0(3) [123.8(3)].
A2*PhBr in that the four characteristic anthracene peaks
between 7 and 8 ppm had condensed to a single multiplet.
Additionally, new proton peaks were observed; firstly, an
ethylene resonance of integration 1 proton was observed
at 6.16 ppm along with two new methylene resonances at
3.9 ppm with integration of 4 protons. The rearranged
structure was confirmed by X-ray crystallographic analysis
of a Ru(dppm)Cl complex, A2*L[Ru]. This complex was
prepared in two steps by first forming the vinylidene species
by addition of A2*L to a solution of NaPF6 and
Ru(dppm)2Cl2 in DCM. This complex was then deproto-
nated with DBU (1,8-diazabicyclo[5.4.0]undec-7-ene) to
yield the desired acetylide complex [7].
As revealed by the X-ray structure of A2*L[Ru], the
ligand synthesis had not progressed as expected to give
the anthracene containing compound A2L but a 10-hydro-
anthracene containing molecule instead. Complexation of
the latter to the ruthenium centre is via the ethynyl carbon
atom to give the complex illustrated in Fig. 5. The geome-
try at the metal centre is distorted octahedral with cis
angles in the range 70.99(5)–108.96(5)ꢁ, the acute angles
corresponding to the bite of the phosphine ligands (Table
Fig. 3. The packing of the molecules in the structure of A1L showing the
˚
extensive C–Hꢁ ꢁ ꢁp interactions. These interactions have: [Hꢁ ꢁ ꢁp (A), [C–
Hꢁ ꢁ ꢁp (ꢁ), (a) 2.99, 138; (b) 2.94, 141; (c) 2.68, 164; (d) 3.07, 144; (e) 2.98,
139; (f) 2.69, 137; (g) 2.62, 161; (h) 2.96, 145.
the Wittig reaction as for A1L. Initially, this reduction was
attempted by dissolving a precursor to A1L, A1PhBr, 9-[2-
(4-bromo-phenyl)-vinyl]-anthracene, in a mixture of meth-
anol and diethyl ether followed by addition of magnesium
turnings [6]. As the magnesium dissolved, liberating hydro-
gen gas, the colour of the initially yellow/fluorescent green
solution diminished in intensity to be colourless after 30–
60 min. Following an acidic workup and purification via
column chromatography, compound A2*PhBr, 9-[2-(4-
bromo-phenyl)-ethylidene]-9,10-dihydro-anthracene, was
isolated. Notably this compound, whilst having been
reduced to the required degree for A2L, had rearranged
to yield a compound with a 9,10-dihydro-anthracenyl
antenna rather than the desired 9-anthracenyl species. This
1). The ‘equatorial’ RuP4 atoms are coplanar to within
0.03 A and the Clꢁ ꢁ ꢁC(1) vector is inclined by ca. 83ꢁ to this
˚
plane. The Ru–P, Ru–Cl, Ru–C(1), C(1)„C(2) and C(2)–
C(3) bond lengths (Table 1), do not differ significantly from
those observed in other related chloro-phenylacetylene-
bis(bis(diphenylphosphino)methane)ruthenium containing
complexes [8]. It is noteworthy that in these related com-
plexes the Clꢁ ꢁ ꢁC(ethynyl) vector is also significantly
inclined to the normal of the RuP4 plane. The only inter-
molecular packing interaction of note is a weak p–p stack-
ing of the C(19)–C(24) rings of centrosymmetrically related
molecules; the centroidꢁ ꢁ ꢁcentroid and mean interplanar
˚
separations are 4.45 and 3.42 A, respectively.
As the ligand rearrangement may have been due to
either a specific problem with the method of reduction or
1
rearrangement was apparent in the H NMR spectrum of

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I. Cade et al. / Journal of Organometallic Chemistry 691 (2006) 1389–1401
A2*L
A1PhBr
A2*PhBr
TMSA, Pd(PPh3)2,
CuI, DIPA
Mg/MeOH
30 min
Br
Br
5 h, 75 %
THF:BH3,
Dioxane,
MeOH
A2PhBr
A2L
TMSA, Pd(PPh3)2,
CuI, DIPA
BR2
Br
Br
5 h, 75 %
H
H2O2,
NaOH(aq)
'TMSI solution'
OH
Br
Fig. 4. Syntheses of A2L and A2*L. Notably, whilst only one isomer is shown above, the hydroboration of A1PhBr produced both regioisomers of the
product borane, with the boron atom at both the anthracenyl and phenyl ends of the linker.
Fig. 5. Structure of compound A2*L[Ru]. Note the sp3 hybridised C(18) and sp2 hybridised C(10).
an intrinsic instability of the ethyl linker when placed
between anthracenyl and phenyl rings, an alternative
two-step reduction was developed (Fig. 4). In the event
of the ethyl linker being intrinsically unstable, this would
allow isolation of an intermediate compound with a
reduced linker moiety. The two-step reduction took the
form of first hydroborating the ethenyl linker of A1PhBr
with a THF solution of freshly prepared THF:BH3 [9,10],
followed by an oxidative cleavage of the carbon–boron
bond using aqueous solutions of potassium hydroxide
and hydrogen peroxide. This yielded a mixture of regioi-
somers of the expected secondary alcohol, which were both
reduced with trimethylsilyl iodide (TMSI) [11–13] to give
A2PhBr, which was then converted to the desired A2L by
coupling TMSA to the 4-position of the phenyl ring using
Sonogashira conditions. The ligand A2L was isolated as a
colourless oil, which solidified upon standing. The 1H
NMR spectrum for this compound showed the expected
anthracene and ethynyl proton peaks. However, the peaks
due to the ethyl linker’s methylene protons were of partic-
ular interest. These were, rather than the expected triplets,
relatively complex multiplets similar to triplet signals with
additional internal fine structure – presumably due to
restricted rotation around the linker bonds vide infra.

I. Cade et al. / Journal of Organometallic Chemistry 691 (2006) 1389–1401
1393
Table 1
Selected bond lengths (A) and bond angles (ꢁ) for A2*L[Ru]
Table 2
1H NMR data for those ligands with linkers possessing protons pertaining
to the behaviour of the individual methylene units within the linker
˚
Ru–Cl
2.5033(11)
Ru–P(1)
2.3684(14)
Ligand
Position of methylene in linker
Ru–P(2)
Ru–P(4)
C(1)–C(2)
C(6)–C(9)
C(10)–C(11)
2.3269(13)
2.3124(13)
1.198(7)
1.554(8)
1.354(11)
Ru–P(3)
Ru–C(1)
C(2)–C(3)
C(9)–C(10)
2.3498(14)
1.999(5)
1.450(7)
Anthracenyl
Central
Phenyl
A1L
A2L
A3L
7.95 (16.6)
3.88 (m)
3.60 (pt)
–
–
6.94 (16.5)
3.09 (m)
2.88 (t)
1.440(11)
2.14 (m)
3JH–H coupling is noted for A1L and is shown in brackets, pt – pseudo
triplet.
C(1)–Ru–P(4)
P(4)–Ru–P(2)
P(4)–Ru–P(3)
C(1)–Ru–P(1)
P(2)–Ru–P(1)
C(1)–Ru–Cl
P(2)–Ru–Cl
P(1)–Ru–Cl
C(1)–C(2)–C(3)
C(11)–C(10)–C(9) 133.4(10)
85.6(2)
178.59(5)
71.05(5)
94.6(2)
70.99(5)
178.02(14)
85.77(5)
83.51(4)
176.7(6)
C(1)–Ru–P(2)
C(1)–Ru–P(3)
P(2)–Ru–P(3)
P(4)–Ru–P(1)
P(3)–Ru–P(1)
P(4)–Ru–Cl
P(3)–Ru–Cl
C(2)–C(1)–Ru
C(10)–C(9)–C(6) 113.4(6)
93.0(2)
82.9(2)
108.96(5)
108.94(5)
177.54(4)
95.63(5)
98.95(4)
177.4(5)
Table 3
˚
Selected bond lengths (A) and bond angles (ꢁ) for A3L
C(6)–C(9)
1.518(7)
1.522(7)
1.542(7)
1.505(7)
C(60)–C(90)
1.564(8)
1.478(9)
1.522(8)
1.503(7)
C(9)–C(10)
C(10)–C(11)
C(11)–C(12)
C(90)–C(100)
C(100)–C(110)
C(110)–C(120)
C(6)–C(9)–C(10)
C(9)–C(10)–C(11)
C(12)–C(11)–C(10)
112.5(4)
112.6(4)
111.0(4)
C(60)–C(90)–C(100)
C(90)–C(100)–C(110)
C(120)–C(110)–C(100)
113.1(6)
110.5(6)
114.1(4)
2.5. Synthesis of A3L
The propyl linker of compound A3L was prepared by
coupling 9-acetylanthracene and 4-ethynylbenzaldehyde
using sodium hydroxide in ethanol via an Aldol reaction
[14]. This proceeded smoothly to yield the desired diaryl
a,b-unsaturated ketone intermediate A(enone)PhBr. This
unsaturated linker was reduced firstly to the secondary
alcohol, by reaction of sodium borohydride in a dioxane/
ethanol mixture [15], followed by reduction to the desired
A3L using TMSI. A3L was also isolated as a colourless
oil, which solidified upon standing. On this occasion, how-
ever, the compound solidified as a mat of needle-like crys-
tals suitable for X-ray structure determination vide infra.
methylene protons gave a complex multiplet signal while
the other linker protons gave peaks with the expected mul-
tiplicities. This is rationalised in terms of less steric hin-
drance allowing greater rotational freedom of these
methylene groups, and resulting in the idealised triplet
and quintet splitting patterns (Table 2). A single crystal
X-ray analysis showed compound A3L to have crystallised
with two independent molecules A and B in the unit cell
(Table 3). These molecules have distinctly different confor-
mations, with in A the C–CH2–CH2–CH2–C backbone
linking the two ring systems having an all-anti conforma-
tion, whereas in B the conformation about one of these
bonds [C(100)–C(110)] is gauche (Fig. 6). The torsional
twists about the C(6)–C(9) and C(11)–C(12) bonds in A
are ca. 68ꢁ and 86ꢁ, whilst their counterparts in B are ca.
1
The H NMR spectrum for this compound showed some
similarities to that of A2L with the addition of a third peak
at 2.14 ppm due to the central methylene protons of the
linker. However, in the case of A3L only the anthracenyl-
˚
Fig. 6. The pair of independent molecules in the structure of A3L. The C–Hꢁ ꢁ ꢁp interactions have: [Hꢁ ꢁ ꢁp (A), [C–Hꢁ ꢁ ꢁp (ꢁ), (a) 2.61, 171; (b) 2.87, 164.

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I. Cade et al. / Journal of Organometallic Chemistry 691 (2006) 1389–1401
Table 5
64ꢁ and 73ꢁ. Molecule B is disordered, there being a minor
occupancy (30%) overlapping conformer where the signs of
the torsional angles about the bonds linking the two ring
systems are reversed. Surprisingly, there are no p–p stack-
ing interactions involving either the phenyl or anthracene
ring systems. The only intermolecular interactions of note
are a pair of C–Hꢁ ꢁ ꢁp interactions between the terminal
ethynyl hydrogen atoms in molecules A and B and one of
the C6 rings of the anthracene units of B and A, respec-
tively (Fig. 6).
Comparison of the 1H NMR acetylenic proton shifts of A0L and A1L with
those of 1,4-diethynylbenzene and 4-ethynylstyrene, respectively
Compound
Acetylene
proton d/ppm
Difference vs.
standard/ppm
Difference vs.
EB/ppm
EB
DEB
3.07
3.16
3.22
3.11
3.17
+0.09
+0.15
+0.04
+0.10
A0L
4-Ethynylstyrene
A1L
+0.06
+0.06
Additionally, comparisons of all the compounds are made with
ethynylbenzene.
3. Trends in the spectroscopic data for the anthracene-
containing linear ligands
with saturated linkers, clearly the chemical shift of the ter-
minal acetylenic protons in A(0–1)L should also be affected
by the p-conjugated linker group. Therefore, to differenti-
ate between the intrinsic effects of the linker groups from
their ability to conduct the effect of the attached anthra-
cene, comparisons of A0L and A1L with diethynylbenzene
(DEB) and ethynylstyrene were made (Table 5). On initial
examination of the data, it may be seen that the linker
groups have relatively large different effects on the terminal
ethynyl group. Comparison of EB, DEB and 4-ethynylsty-
rene shows that the inclusion of an additional ethynyl
group causes a downfield shift of the ethynyl protons more
than twice as large as that caused by the addition of an eth-
enyl group, +0.09 ppm vs. +0.04 ppm, respectively.
It is interesting to note that from the data shown in
Table 5, the acetylenic proton shifts of A0L and A1L
appear to be equally affected by the presence of an attached
anthracene, approximately +0.06 ppm. It was thought that
the two unsaturated linkers would provide different degrees
of conjugation between antenna and core moieties. How-
ever, this unexpected result may have its origins in the dif-
fering flexibility of the two linkers in combination with
their degree of unsaturation.
1
3.1. H NMR of the terminal ethynyl and linker protons
It is worth noting spectroscopic trends in the behaviour
of the linear ligands, A(0–3)L. Of particular interest is the
effect the pendant anthracene has on the terminal acetylene
groups and the extent that the central linker mediates this.
1H NMR has been used to examine the acetylene protons
for the ligands A(0–3)L and the data are displayed below
(Table 4) (ethynylbenzene, EB was used as a standard aro-
matic substituted terminal acetylene for comparison).
From these results, it is worthy of note that the acetylene
protons of the ligands with saturated linkers A(2–3)L
appear unaffected by the addition of a pendant anthracene,
or indeed addition of the saturated linker. This is not so
surprising as the saturated linker effectively insulates the
ethynyl benzene moiety from the p-system of anthracene,
which should otherwise interact strongly with the p-system
of the ethynyl benzene core. However, this is not necessar-
ily a trivial result, as although the alkyl linker cannot inter-
act via p-conjugation with the core ethynyl benzene it is r-
electron donating and may have had an observable effect
on the electronics of the core. Additionally, it is possible
that such flexible linkers, especially in the case of A3L,
might allow a through space, rather than through bond,
interaction between the terminal acetylene and anthracene
3.2. IR spectroscopy of the ethynyl groups
1
In addition to H NMR, the IR behaviour of ligands A
1
p-system. In contrast to the H NMR spectra of A(2–3)L,
(0–3)L, in particular the ethynyl groups, was examined and
1
those of the ligands with unsaturated linkers, A(0–1)L,
show distinct variation of the ethynyl proton signal
compared to that of EB. Both ligands possess extended p-
is tabulated below (Table 6). In contrast to the H NMR
data collected for these ligands, there appears to be very lit-
systems throughout their structures allowing for
a
through-bond interaction between the anthracenyl and ethy-
nyl groups to occur. However, in contrast to those ligands
Table 6
Combined IR data for A(0–3)L relating to the properties of the terminal
acetylene groups in each case and compared with that of ethynylbenzene
(EB)
Table 4
Combined 1H NMR data for A(0–3)L relating to the properties of the
terminal acetylene groups in each case, compared with that of ethynyl-
benzene (EB)
Compound m„CH/cmꢀ1 Difference vs. mC„C/cmꢀ1 Difference vs.
EB/cmꢀ1
EB/cmꢀ1
EB
3294
3296
3295
3299
3298
2111
A0L
A1L
A2L
A3L
a
+2
+1
+5
+4
2110a
ꢀ1
Compound
Acetylene proton d/ppm
Difference vs. MEB/ppm
2105
b
ꢀ6
EB
3.07
3.22
3.17
3.07
3.07
b
A0L
A1L
A2L
A3L
0.15
0.10
0.00
0.00
2109
ꢀ2
Internal C„C bond stretch occurs at 2196.0 cmꢀ1
.
b
Peak too weak and not observed.

I. Cade et al. / Journal of Organometallic Chemistry 691 (2006) 1389–1401
1395
tle variation across the series of compounds associated with
the ethynyl groups. The variation in the stretching fre-
quency of the terminal acetylenic C–H bond varies by less
than five wavenumbers between ethynylbenzene and the
ligands. However, the ligands do seem to fall into two
groups, based upon C–H stretching frequency, those with
p-conjugated linkers and those with saturated hydrocarbon
linkers. These two groups display C–H stretching
frequencies approximately the same as, and 4 cmꢀ1 higher
in energy than the standard EB, respectively. The variation
in the C„C stretching frequency is slightly larger,
however, as the peaks associated with these IR absorptions
are typically very weak the error associated with
their energies is greater than that for the C–H bond
stretches.
3.3. ‘T’-shaped ligand syntheses
˚
Fig. 7. The molecular structure of A1T. Selected bond lengths (A) and
bond angles (ꢁ); C(2)–C(9) 1.467(3), C(9)–C(10) 1.320(3), C(10)–C(11)
1.476(3), C(2)–C(9)–C(10) 125.8(2), C(9)–C(10)–C(11) 126.9(2).
Compounds 9-[2-(2,5-diethynyl-phenyl)-vinyl]-anthra-
cene (A1T), 9-[2-(2,5-diethynyl-phenyl)-ethyl]-anthracene
(A2T) and 9-[3-(2,5-diethynyl-phenyl)-propyl]-anthracene
(A3T) were prepared as for their linear analogues, however,
in these cases the required benzaldehyde precursor was not
commercially available and was instead prepared via chro-
mium(VI)oxide/sulphuric acid oxidation of 2,5-dibromo-
toluene [16]. This oxidation was carried out in a mixture
of acetic acid and acetic anhydride in order to avoid over
oxidation to 2,5-dibromobenzoic acid. The initial step
yielded a diester, which was then hydrolysed by heating
in a solution of H2SO4 in a mixture of water and ethanol
4. Trends in the spectroscopic data for the the ‘T’-shaped
ligands A(1-3)T
1
4.1. H NMR of the terminal ethynyl and linker protons
As for the linear ligands, it is useful to compare the spec-
tral properties of this new set of ‘T’-shaped ligands. Again,
to gauge the effect of the linker upon communication
between the antennae to the rest of the ligand, the 1H
NMR resonances associated with the ethynyl protons are
of interest (Table 7). Worthwhile comparisons of these data
include the variation of the peak positions relative to those
of 1,4-diethynylbenzene, DEB. Such a comparison shows
that the ppm values for the high field proton signals for
all the ligands are quite similar to the single resonance from
DEB. This suggests that the ethynyl protons associated
with this high field peak are all likely to be in the meta-posi-
tion to the linker, resulting in little communication between
it and the antenna-linker moiety. This has indeed been con-
firmed by recording spectra of mono-ethynylated deriva-
tives of A2T of known substitution pattern. Additionally,
it is notable that the high field ethynyl protons of A2T
and A3T are not exactly the same, as would be expected
for a system where the only antenna-ethynyl proton com-
munication is via the linker. This suggests that there may
be some other, possibly through-space, interaction between
the anthracene and/or linker group and the ethynyl group
in either A2T or A3T. Additionally for A(2–3)T compari-
son of the low-field ethynyl proton resonances also shows
some unusual patterns. Despite the apparently near identi-
cal electronic environments of the two sets of ethynyl
groups, the low field resonance of A2T is significantly dif-
ferent from that of A3T (+0.32 and +0.11 ppm vs. DEB,
respectively).
1
to yield the desired aldehyde. This had the expected H
NMR resonances at 10.3, 8.0 and 7.6 ppm for the aldehyde
and phenyl ring protons, respectively.
In addition to having to prepare the benzaldehyde pre-
cursor, the ‘T’-shaped ligands displayed different behaviour
than their linear analogues with respect to the coupling of
TMSA to the core phenyl ring. In the case of the linear
ligands this reaction proceeded smoothly, completing within
12 h and often in considerably less time. However, for the
‘T’-shaped precursors this reaction proved to be unexpect-
edly troublesome, often resulting in only partial reaction
despite extended reaction times and greater than stoichiom-
etric quantities of TMSA. This difficulty is ascribed to the
greater steric crowding associated with reaction ortho and
meta rather than para to the antenna-linker group.
In its X-ray crystal structure determination, ligand A1T
crystallises with only one independent molecule in the unit
cell and has a conformation very similar to those observed
for 2 (Fig. 7). The torsional twists about the C(2)–C(9) and
C(10)–C(11) bonds are 17ꢁ and 50ꢁ, respectively, the phenyl
and anthracene ring systems being mutually inclined by ca.
68ꢁ (cf. 52ꢁ and 61ꢁ for the two independent molecules of
A1L). The intermolecular packing interactions are fairly
complex; symmetry related molecules are linked by C–
Hꢁ ꢁ ꢁp interactions to form corrugated sheets (Fig. 8a)
and adjacent sheets are linked by a combination of C–
Hꢁ ꢁ ꢁp and p–p stacking interactions (Fig. 8b).
A possible explanation for this unexpected behaviour
may involve one of the ethynyl protons in A2T being able

1396
I. Cade et al. / Journal of Organometallic Chemistry 691 (2006) 1389–1401
Fig. 8. (a) Part of one of the C–Hꢁ ꢁ ꢁp linked corrugated sheets in the structure of A1T. (b) The C–Hꢁ ꢁ ꢁp and p–p stacking interactions that link adjacent
˚
sheets. The C–Hꢁ ꢁ ꢁp interactions have: [Hꢁ ꢁ ꢁp] (A), [C–Hꢁ ꢁ ꢁp] (ꢁ), (a) 2.74, 163; (b) 3.00, 161; (c) 2.88, 143; (d) 3.01, 174. The pꢀp stacking interactions
˚
˚
have centroidꢁ ꢁ ꢁcentroid separations (e) and (f) of 3.85 A and the mean interplanar separation between the anthracene rings is 3.60 A.
Table 7
associated with the ethynyl groups. However, the slight
1H NMR data associated with the ethynyl proton resonances for the ‘T’-
decrease in stretching frequency of the C„C group for
shaped ligands
all ligands relative to DEB may indicate a very small reduc-
tion in triple bond character for the ligands. Another nota-
Compound High field acetylene Low field acetylene Peak
proton d/ppm
proton d/ppm
separation/ppm
ble feature is that despite the presence of two chemically
distinct ethynyl groups, there is only one carbon–carbon
triple bond and one ethynyl proton stretching frequency
for all but one compound, A2T. In the case of A2T there
appears to be a distinct shoulder on the peak associated
with the carbon–carbon triple bond stretch. This is taken
to be further supporting evidence for the anomalous varia-
tion in the two ethynyl groups of A2T vide supra.
DEB
A1T
A2T
A3T
3.16
3.25 (+0.09)
3.22 (+0.06)a
3.16 (0.00)
3.33 (+0.19)
3.48 (+0.32)b
3.25 (+0.11)
0.08
0.26
0.09
Numbers in parentheses are the differences between the 1H NMR reso-
nances due to each ligand and the standard 1,4-diethynylbenzene.
a
Determined to be due to the meta-ethynyl group.
Determined to be due to the ortho-ethynyl group.
b
to interact through space with the anthracene moiety. This
interaction may take the form of a hydrogen bond between
the ethynyl and anthracenyl groups. This type of bonding
has already been observed in the X-ray structures of the
anthracene containing ligands.
5. Conclusions
A range of anthracene-functionalised 4-ethynyl- and
1,4-diethynylbenzene compounds have been prepared and
characterised with respect to their solution state 1H
NMR and IR spectral properties. The linear and ‘T-
shaped’ ligands were prepared via similar synthetic routes
based upon the formation of the anthracene–phenyl ring
linker via either Sonogashira, Wittig, or Aldol reactions.
These initially formed linker moieties were further modified
to yield the desired two- and three-carbon saturated and
unsaturated hydrocarbon linkers. Sonogashira conditions
were also used to couple terminal ethynyl groups to the
core phenyl rings. In the preparation of the ethyl linker
of A2L an unusual rearrangement of the anthracene moiety
was observed. This involved the formation of an ethyli-
dene-substituted 9,10-dihydro-anthracene group from a 9-
ethenyl-anthracene precursor.
NMR analysis of the terminal ethynyl protons showed
that the nature of the linker moiety has a significant effect
on the degree of interaction between the anthracenyl
antenna and the core ethynyl benzene moieties. Most nota-
bly, while the propyl and ethyl linkers should confer near
identical electronic properties to their respective ligands
1H NMR analysis shows that the terminal ethynyl protons
4.2. IR spectroscopy of the ethynyl groups
As for the linear ligands comparisons of the IR spectra
of the ‘T’-shaped ligands may also be made with particular
respect to the ethynyl groups (Table 8). As for the linear
ligands there is only a little variation in the IR peaks
Table 8
IR peaks associated with the ethynyl groups of the ‘T’-shaped ligands
Compound m„CH/cmꢀ1 Difference vs. mC„C/cmꢀ1 Difference vs.
DEB/cmꢀ1
MEB/cmꢀ1
DEB
A1T
A2T
A3T
3297
3300
3297
3298
2111
2105
2105/2108a
2107
+3
0
+1
ꢀ6
ꢀ6/ꢀ3
ꢀ4
The differences in peak positions relative to those for diethynylbenzene
(DEB) are also shown for comparison.
a
Two values are given because, uniquely for A2T there were two peaks
observed (a peak with a disinct shoulder).

I. Cade et al. / Journal of Organometallic Chemistry 691 (2006) 1389–1401
1397
of A2T and A3T have different electronic environments. In
addition to H NMR and IR analysis it was observed that
cooled to 0 ꢁC and stirred for 15 min. 1,4-Diethynyl ben-
zene (189 mg, 1.5 mmol) was added and the mixture was
heated to reflux for 15 h. The solvent was removed under
vacuum and the resulting mixture was washed with 10%
HCl solution (50 ml), water (50 ml), saturated sodium
bicarbonate solution (50 ml) and water (50 ml). The trim-
ethylsilyl-protected product was obtained pure from silica
column chromatography (95:5 hexane:dichloromethane).
1
both the ligands possessing unsaturated and saturated link-
ers displayed a strong fluorescence, in the visible and near
UV region, respectively. The detailed analysis of this fluo-
rescent behaviour of both these groups of ligands, and their
coordination to Pt metal centres will be presented in a
forthcoming paper.
1
Yield: 210 mg, 70%. H NMR d/ppm: 8.61 (2H d Anth),
6. Experimental
8.42 (1H s 10-Anth), 8.00 (2H d Anth), 7.69 (2H d Anth),
7.53 (6H m 2/3-Anth + Ph), 3.22 (1H s a-CCH). 13C NMR
d/ppm: 132.66, 132.22, 131.47, 131.18, 128.74, 128.08,
126.74, 126.63, 125.72, 124.10, 122.06, 116.84, 100.14,
88.40, 83.35, 79.04. Mass, m/z: 302 (M+), 274 (–CCH),
124 (1,4-diethynylbenzene). IR/cmꢀ1: 3295.8 m(CC–H),
2196.0 m(ArC„CAr0), 2109.9 m(C„CH). UV/nm: 10ꢀ5 M
DCM. 428 (0.247), 404 (0.270), 313 (0.346), 299 (0.184),
266 (1.129). Elemental analysis: Calc. for C24H14: C,
95.33; H, 4.67. Found: C, 95.56, H, 4.63%.
6.1. General
All reactions were performed under a nitrogen atmo-
sphere using standard schlenk techniques and all solvents
were distilled over standard drying agents unless otherwise
stated. All reagents were used as purchased from either
Aldrich Chemical Company, Lancaster or Acros without
purification. Silica gel (60 grade) was used for all column
chromatographic separations 1H NMR and 13C NMR
spectral were recorded using a Delta upgrade on a JEOL
7.2. 9-(2-(4-Ethylnylphenyl)ethenyl)anthracene (A1L)
EX 270 MHz spectrometer. H, 13C and 31P NMR chemi-
1
cal shifts are reported relative to CDCl3 (residual proton
7.2.1. 4-(2-Trimethylsilylethynyl)benzaldehyde
1
impurities H = d 7.26 ppm, 13C = d 77 ppm) and H3PO4
4-Trimethylsilylethynylbenzaldehyde was prepared from
4-bromobenzaldehyde (310 mg, 2 mmol) and trimethylsilyl
acetylene (0.3 ml, 2.2 mmol), using a Heck coupling proce-
dure as used for A0L. Silica column chromatography
(DCM:hexane, 10:90) yielded the desired product. Yield:
(31P = d 0.00 ppm). Data are shown with assignments for
which atoms are thought to be responsible for a particular
peak. IR spectra were recorded on a Perkin–Elmer FT-IR
spectrometer from samples in DCM solution. Analysis of
IR spectra is limited for the most part to the effects of sub-
stitution on the strength of the carbon–carbon triple bond.
Thus, the peaks quoted below refer to the carbon–proton
and carbon–carbon stretches at approximately 3300 and
2100 cmꢀ1, respectively, UV–Vis spectra were recorded
using a Thermo Electron Corporation Nicolet Evolution
100 absorption spectrometer. The absorption spectra are
reported in terms of the wavelength of the peak absorp-
tions and their intensities in parentheses. Mass spectra were
recorded using a micromass Autospec Q spectrometer
using an EI method. The spectra are reported in terms of
the molecular ion and the most significant fragmentation
peaks. Assignment of these peaks is based simply upon
their m/z ratio and formulation of a reasonable fragmenta-
tion mechanism. The exception to this is for the assignment
of the molecular ion peaks, which were additionally identi-
fied using a computerised isotope pattern predictor. X-ray
structural analyses were carried out by Dr. Andrew J.P.
White at the Chemical Crystallographic Laboratory, Impe-
rial College. Elemental analyses were carried out by Ste-
phen Boyer at the London Metropolitan University.
1
360 mg, 89%. H NMR d/ppm: 9.86 (1H s C(O)H), 7.79
(2H d Ph), 7.57 (2H d Ph), 0.24 (9H s TMS). IR/cmꢀ1
:
2158 m(ArC„CTMS).
7.2.2. 9-Bromomethylanthracene
9-Anthracene methanol (1248 mg, 6 mmol) was dis-
solved in dichloromethane (50 ml) and cooled in a dry
ice/acetone bath with stirring. Boron tribromide (0.2 ml,
2 mmol) was added dropwise affording an initially green/
blue suspension which turned brown. This was allowed to
stir at ꢀ78 ꢁC for 1 h and was then warmed to room tem-
perature to complete the reaction. Water (10 ml) was then
added, with stirring, to the cooled solution (ꢀ78 ꢁC), which
was then allowed to warm to room temperature. The
organic layer was separated and washed with 10% aqueous
HCl solution (20 ml), followed by water (20 ml), sodium
bicarbonate solution (20 ml) and water and then dried over
magnesium sulphate. Evaporation of the solvent yielded a
product sufficiently pure for the next step. Yield: 1.45 g,
1
89%. H NMR d/ppm: 8.44 (1H s 10-Anth), 8.29 (2H d
Anth-1), 8.00 (2H d Anth-4), 7.62 (2H m (pt) Anth-2/3),
7.48 (2H m (pt) Anth-3/2), 5.52 (2H s Anth-CH2Br). Mass,
m/z: 270/272 (M+ 79/81Br), 191 (Anth–Me).
7. Synthesis of the linear anthracene-containing ligands
7.1. 9-(2-(4-Ethynylphenyl)ethynediyl)anthracene (A0L)
7.2.3. 9-(Triphenylphosphoniumbromide)methylanthracene
9-Bromomethylanthracene (271 mg, 1 mmol) and triphe-
nyl phosphine (288 mg, 1.1 mmol) were dissolved in toluene
(50 ml) and heated to reflux with stirring for 3 h to yield a
pale yellow suspension. The suspension was filtered off and
9-Bromoanthracene (257 mg, 1 mmol), dichlorobis(tri-
phenylphosphine)palladium (7 mg, 0.01 mmol) and cop-
per(I)iodide (3.9 mg, 0.02 mmol) were dissolved in DIPA

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I. Cade et al. / Journal of Organometallic Chemistry 691 (2006) 1389–1401
washed with several portions of diethyl ether to remove any
unreacted starting material. The desired product was then
obtained after recrystallisation from hot chloroform, as a
reaction. Water (2 ml) was added followed by addition of
a mixture of aqueous hydrogen peroxide (6%, 25 ml) and
sodium hydroxide (3 N, 5 ml) accompanied by an immedi-
ate darkening of the solution. Ether (50 ml) was then added
and the organic layer was separated and washed with water
(3 · 50 ml). The desired products were purified using silica
column chromatography (80:20, hexane:DCM) to yield an
almost equal mixture of the 1- and 2-hydroxyethyl deriva-
1
cream powder. Yield: 455 mg, 85%. H NMR d/ppm: 8.27
(1H d 10-Anth), 7.79 (4H m Anth-1 and Anth-4), 7.49
(16H m Anth + Ph), 7.21 (2H m (pt) Anth-3/2), 7.15 (2H
m (pt) Anth-2/3), 6.15 (2H d [2JH–P 14 Hz] Anth-CH2P).
9-(Triphenylphosphoniumbromide)methylanthracene
(455 mg, 0.85 mmol) and potassium tert-butoxide (105 mg,
0.94 mmol) were dissolved in THF (50 ml) immediately
forming a dark ‘beetroot coloured’ solution. This was
allowed to stir at room temperature for 1 h to complete
the formation of the ylide. A THF (20 ml) solution of 4-
(2-trimethylsilylethynyl)benzaldehyde (122 mg, 0.94 mmol)
was added and the reaction heated to reflux for 3 h yielding
a yellow solution with a blue/green fluorescence. The mix-
ture was cooled to room temperature and then washed with
10% aqueous HCl solution (20 ml), followed by water
(20 ml), sodium bicarbonate solution (20 ml) and water
(20 ml). The trimethylsilyl protected product was obtained
pure after silica column chromatography (80:20, hex-
ane:DCM). The trimethylsilyl group was then removed
using potassium carbonate, as for 1,4-diethynyl benzene,
1
tive. Yield: 626 mg, 67%. H NMR d/ppm: 8.64 (1H br s
C–OH), 8.43 (1H s 10-Anth), 8.28 (1H d Anth), 8.03 (2H
d Anth) 7.55 (6H m Anth + Ph), 7.35 (1H d Anth), 7.20
(1H d Ph) 4.05 (1H m CH–O), 3.90 (1H m CH–O), 3.67
(2H m Anth–CH2), 3.25 (2H m Ph–CH2).
7.3.3. 9-(2-(4-Bromophenyl)ethyl)anthracene
solution of 9-(2-(4-Bromophenyl)20/10-hydroxy-
A
ethyl)anthracene (631 mg, 1.67 mmol) in hexane/dichloro-
methane (5 ml/15 ml) was added to the acetonitrile
solution of freshly prepared TMSI and stirred at room tem-
perature for 1 h. Water was then added and the product
extracted with DCM. The organic layers were then washed
with a saturated aqueous solution of sodium thiosulphate,
to reduce the iodine by-product, followed by water (20 ml).
The DCM solution was then dried over magnesium sul-
phate and evaporated to dryness in vacuo. The desired
product was obtained from silica column chromatography
1
to yield the desired product A1L. Yield. 155 mg, 60%. H
NMR d/ppm: 8.42 (1H d 10-Anth), 8.31 (2H m 4-Anth),
8.00 (2H d 1-Anth), 7.95 (1H d [3JH–H 16.6 Hz] C@C(H)-
Anth), 7.59 (4H m Anth + Ph), 7.49 (4H m Anth + Ph),
6.94 (1H d [3JH–H 16.5 Hz] C@C(H)–Ph) 3.18 (1H s
CCH). 13C NMR d/ppm: 137.8, 136.6, 132.7, 132.4,
131.6, 129.8, 128.8, 126.8, 126.5, 126.3 , 125.9, 125.7,
125.3, 121.6, 83.8, 78.1. Mass, m/z: 304 (M+), 202 (Anth–
CH@CH), 176 (Anth). IR/cmꢀ1: 3294.9 m(CC–H), 2105.2
m(C„4CH). UV/nm: 10ꢀ5 M DCM. 395 (0.120), 560
(1.055). Elemental analysis: Calc. for C24H16: C, 94.70;
H, 5.30. Found: C, 94.53; H, 5.45%.
1
(90:10, hexane:DCM). Yield: 0.49 mg, 81%. H NMR d/
ppm: 8.38 (1H s 10-Anth), 8.24 (2H d Anth), 8.02 (2H d
Anth) 7.50 (6H m Anth + Ph), 7.24 (2H d e-Ph), 3.87
(2H m h-CH2), 3.04 (2H m g-CH2). Mass, m/z: 362/360
(79Br/81Br M+), 191 (Anth–Me).
9-(2-(4-Trimethylsilylethynylphenyl)ethyl)anthracene
was prepared from 9-(2-(4-bromophenyl)ethyl)anthracene
(0.49 mg, 1.36 mmol) and TMSA (0.19 ml, 1.49 mmol)
using a Heck coupling reaction modified from that used
for A0L. Yield: 68%. 1H NMR d/ppm: 8.37 (1H s 10-
Anth), 8.26 (2H d Anth), 8.03 (2H d Anth) 7.49 (6H m
Anth + Ph), 7.27 (2H d e-Ph), 3.88 (2H m h-CH2), 3.08
(2H m g-CH2). Mass, m/z: 378 (M+), 281 (Anth-
CH2CH2Ph), 203 (Anth-CH2CH2). The TMS protecting
group was then removed using potassium carbonate as
for 1,4-diethynylbenzne to yield A2L. Yield: 283 mg,
7.3. 9-(2-(4-Ethynylphenyl)ethyl)anthracene (A2L)
7.3.1. 9-(2-(4-Bromophenyl)ethenyl)anthracene
9-(2-(4-Bromophenyl)ethenyl)anthracene was prepared
as for A1L using 4-bromobenzaldehyde rather than 4-
(trimethylsilylethynyl) benzaldehyde in a Wittig reaction.
1H NMR d/ppm: 8.41 (1H s 10-Anth), 8.31 (2H m 4-Anth),
8.02 (2H d 1-Anth), 7.89 (1H d [3JH–H 16.6 Hz] C@C(H)–
Anth), 7.55 (4H m Anth + Ph), 7.49 (4H m Anth + Ph),
6.87 (1H d [3JH–H 16.5 Hz] C@C(H)–Ph). Mass, m/z:
360/362 (M+ + H 79/80Br), 282 (M+–Br), 191 (Anth–Me),
179 (anth).
1
Quant. H NMR d/ppm: 8.37 (1H s 10-Anth), 8.25 (2H d
Anth), 8.02 (2H d Anth) 7.49 (6H m Anth + Ph), 7.31
(2H d e-Ph), 3.88 (2H m h-CH2), 3.09 (2H m g-CH2),
3.07 (1H s CCH). 13C NMR d/ppm: 143, 133, 132, 131,
129, 129, 128, 126, 126, 125, 124, 120, 84, 77 (hidden
behind CHCl3), 37, 30. Mass, m/z: 306 (M+), 191 (Anth–
Me). IR/cmꢀ1
: 3298.7 m(CC–H).UV/nm: DCM. 390
7.3.2. 9-(2-(4-Bromophenyl)-1/2-hydroxyethyl)anthracene
A solution of iodine (350 mg, 1.38 mmol) in THF
(25 ml) was added slowly dropwise (60 min) to a cooled
solution (0 ꢁC) of sodium borohydride (132 mg, 3.5 mmol)
in THF (25 ml). A THF solution (20 ml) of 9-(2-(4-
bromo)ethenyl)anthracene (897.5 mg, 2.5 mmol) was
added and the mixture stirred at room temperature for
1 h followed by heating to reflux for 4 h to complete the
(0.060), 259 (0.903). Elemental analysis: Calc. for C24H18:
C, 94.12; H, 5.58. Found: C, 93.90; H, 5.65.
7.4. 9-(3-(4-Ethylnylphenyl)propyl)anthracene (A3L)
7.4.1. 9-(3-(4-Bromophenyl)prop-2-enoneyl)anthracene
9-Acetylanthracene (440 mg, 2 mmol) and 4-bromo-
benzaldehyde were dissolved in non-distilled methanol fol-

I. Cade et al. / Journal of Organometallic Chemistry 691 (2006) 1389–1401
1399
lowed by three pellets of sodium hydroxide. The solution
was briefly degassed, by cycling from a vacuum to nitrogen
atmosphere four times, then stirred for 20 h. The resulting
precipitate was filtered off and washed with water and small
portions of methanol, yielding a product sufficiently pure
7.46 (6H m Anth + Ph), 7.22 (2H m Anth), 3.60 (2H t i-
CH2), 3.07 (1H s a-CCH), 2.88 (2H t g-CH2), 2.14 (2H m
h-CH2). 13C NMR d/ppm: 143.0, 134.5, 132.2, 131.6,
129.5, 129.2, 128.5, 125.7, 125.5, 124.7, 124.2, 119.6, 83.8,
76.7. Mass, m/z: 320 (M+), 191 (Anth–Me), 178 (Anth).
IR/cmꢀ1: 3295.1 m(CC–H), 2106.3 m(C„CH). UV/nm:
10ꢀ5 M DCM. 386 (0.112), 256 (1.484). Accurate mass
Calc. for C25H20 320.1554. Found: 320.156501%.
1
for the next step. Yield: 718 mg, 93%. H NMR d/ppm:
8.54 (1H s Anth), 8.05 (2H m Anth), 7.88 (2H m Anth),
7.47 (6H m Anth + Ph), 7.26 (3H m Ph + C@CH), 7.15
(1H d C@CH).
8. Synthesis of the ‘T’-shaped anthracene-containing ligands
7.4.2. 9-(3-(4-Bromophenyl)-1-hydroxypropyl)anthracene
9-(3-(4-Bromophenyl)prop-2-enoneyl)anthracene (718
mg, 1.85 mmol) was dissolved in a mixture of non-distilled
dioxane (30 ml) and methanol (10 ml) followed by sodium
borohydride (280 mg, 7.42 mmol). The mixture was briefly
degassed as above and refluxed under nitrogen for 1 h.
Water (10 ml) was then added to quench unreacted sodium
borohydride and the solvent mixture was reduced in vol-
ume in vacuo. Ether was added and the organic layers
washed with 10% aqueous HCl (20 ml), water (20 ml), sat-
urated sodium bicarbonate solution (20 ml) and water
(20 ml). The resulting oil was sufficiently pure for the next
step. Yield: 704 mg, quantitative.
8.1. 9-(2-(2,5-Diethynylphenyl)ethenyl)anthracene (A1T)
8.1.1. 2,5-Dibromobenzaldehyde
2-5-Dibromotoluene (0.552 ml, 4 mmol) was dissolved
in a mixture of acetic acid (10 ml) and acetic anhydride
(26 ml) and cooled in an ice/water bath. Chromium(VI)
oxide (996 mg, 10 mmol) and sulphuric acid (0.85 ml,
16 mmol) were then added to this vigorously stirred cooled
solution, which was stirred for a further 1 h. The reaction
mixture was then poured into ice/water (approx. 50 ml)
and neutralised by careful addition of sodium bicarbonate
with vigorous stirring. The diester product (see discussion)
was filtered off and recrystallised from hot petroleum ether.
Yield: 1098 mg, 75%. This was then dissolved in a mixture
of water (10 ml) ethanol (20 ml) and sulphuric acid (1 ml)
and heated to 75 ꢁC for 80 min, upon cooling the desired
product was filtered off, sufficiently pure for the next step.
Yield: 637 mg, 80%. 1H NMR d/ppm: 10.27 (1H s C(O)H),
8.01 (1H d Ph), 7.55 (2H m Ph).
1H NMR d/ppm: 8.51 (1H br s OH), 8.39 (1H s Anth),
7.99 (2H m Anth), 7.42 (7H m Anth + Ph), 7.07 (2H d Ph),
6.22 (1H m Anth) 2.90 (1H m CH–O), 2.78 (3H m Ph–
CH2) 2.35 (1H m CH2). Mass, m/z: 390/392 (79Br/81Br
M+), 205/208 (Anth–Me–OH), 178 (Anth).
7.4.3. 9-(3-(4-Bromophenyl)propyl)anthracene
TMSI (16.2 mmol) was prepared as for A2L into which
9-(3-(4-bromophenyl)-1-hydroxypropyl)anthracene (1.07 g,
2.7 mmol) was added as a hexane/DCM solution (5 ml/
15 ml). The reaction was allowed to stir for 1 h at room
temperature. Water (10 ml) was then added and the prod-
uct extracted with DCM. The organic layers were then
washed with a saturated aqueous solution of sodium thio-
sulphate, to reduce the iodine by-product, followed by
water (20 ml). The DCM solution was then dried over mag-
nesium sulphate and evaporated to dryness in vacuo. Silica
column chromatography (80:20, hexane:DCM) yielded the
desired product. Yield: 828 mg, 78%. 1H NMR d/ppm: 8.32
(1H s Anth), 8.12 (2H d Anth), 8.00 (2H d Anth), 7.44 (6H
m Anth + Ph), 7.13 (2H m Ph), 3.60 (2H t Anth–CH2), 2.83
(2H t Ph–CH2), 2.11 (2H m CH2). Mass, m/z: 374/376
(79Br/81Br M+), 191 (Anth–Me), 178 (Anth).
8.1.2. 2,5-Bis(trimethylsilylethynyl)benzaldehyde
2,5-Dibromobenzaldehyde (387 mg, 1.5 mmol) and
TMSA (0.5 ml, 3.6 mmol) were coupled via a Sonogashira
reaction and purified via silica column chromatography
(DCM:hexane, 20:80) to yield the desired product. Yield:
1
357 mg, 80%. H NMR d/ppm: 10.47 (1H s C(O)H), 7.94
(1H s Ph), 7.50 (2H m Ph), 0.24 (18H s TMS).
9-(Triphenylposphoniumbromide)methylanthracene
(343 mg, 0.64 mmol) and potassium tert-butoxide (78 mg,
0.71 mmol) were dissolved in THF (20 ml). This was
allowed to stir at room temperature for 1 h to complete
the formation of the ylide. A THF (20 ml) solution of
2,5-bis(trimethylsilylethynyl) benzaldehyde (202.6 mg,
0.68 mmol) was added and the reaction treated as for
A1L. Mass, m/z: 472 (M+), 454 (–Me), 441 (ꢀ2 · Me),
399 (–TMS), 302 (ꢀ2 · TMS).
9-(2-(4-Trimethylsilylethynylphenyl)propyl)anthracene
was prepared from 9-(2-(4-bromophenyl)propyl)anthra-
cene (845 mg, 2.25 mmol) and TMSA (0.34 ml, 2.48 mmol)
using a Heck coupling reaction modified from that used for
The trimethylsilyl group was then removed using potas-
sium carbonate, as for 1,4-diethynyl benzene, to yield the
desired product A1T. 1H NMR d/ppm: 8.42 (1H s 10-Anth),
8.37 (2H m 4-Anth), 8.02 (5H m j + 1-Anth), 7.49 (7H m
d,e,g + 2,3-Anth), 7.31 (1H d [3JH–H 7.3 Hz] i), 3.33 (1H s
a), 3.25 (1H s a0). 13C NMR d/ppm: 139.7, 134.3, 133.3,
132.1, 131.5, 130.8, 129.7, 128.7, 128.1, 126.8, 125.9,
125.7, 125.2, 122.9, 121.5, 83.8, 83.1, 81.5, 79.1. Mass, m/
z: 328 (M+), 304 (–CCH), 151 (–Anth). IR/cmꢀ1: 3299.7
m(CC–H), 2105.4 m(C„CH). UV/nm: 10ꢀ5 M DCM. 392
1
A0L. H NMR d/ppm: 8.33 (1H s 10-Anth), 8.12 (2H d
Anth), 8.00 (2H d Anth), 7.46 (6H m Anth + Ph), 7.22
(2H m Anth), 3.59 (2H t i-CH2), 2.88 (2H t g-CH2), 2.13
(2H m h-CH2), 0.30 (TMS). The protecting group was then
removed using potassium carbonate as for 1,4-diet-
1
hynylbenzne to yield the product A3L. H NMR d/ppm:
8.33 (1H s 10-Anth), 8.12 (2H d Anth), 8.00 (2H d Anth),

1400
I. Cade et al. / Journal of Organometallic Chemistry 691 (2006) 1389–1401
(0.514), 249 (3.11). Elemental analysis: Calc. for C26H16: C,
95.12; H, 4.88. Found: C, 95.28; H, 4.68%.
NMR d/ppm: 144.0, 133.1, 132.5, 131.6, 129.8, 129.6,
129.2, 126.1, 125.5, 124.8, 124.3, 99.9, 83.2, 82.5, 78.9.
Mass, m/z: 330 (M+), 191 (Anth–Me), 179 (Anth). IR/
8.2. 9-(2-(2,5-Diethylnylphenyl)ethyl)anthracene (A2T)
cmꢀ1
: 3296.6 m(CC–H), 2107.5 m(C„CH). UV/nm:
10ꢀ5 M DCM. 391 (0.393), 370 (0.426), 275 (0.896), 251,
(2.687). Elemental analysis: Calc. for C26H18: C, 94.55;
H, 5.46. Found: C, 94.78; H, 5.81%.
8.2.1. (2-(2,5-Dibromophenyl)ethenyl)anthracene
9-(Triphenylphosphoniumbromide)methylanthracene
(3.198 g, 6 mmol) and potassium tert-butoxide (672 mg,
6 mmol) were dissolved in THF (50 ml). This was allowed
to stir at room temperature for 1 h to complete the forma-
tion of the ylide. A THF (20 ml) solution of 2,5-dibromo-
benzaldehyde (1.584 g, 6 mmol) was added and the
8.3. 9-(2-(2,5-Diethynylphenyl)propyl)anthracene (A3T)
8.3.1. 9-(3-(2,5-Dibromophenyl)prop-2-enoneyl)anthracene
9-(3-(2,5-Dibromophenyl)prop-2-enoneyl)anthracene
was prepared by reacting 9-acetylanthracene (634 mg,
2.88 mmol) with 2,5-dibromo benzaldehyde (637 mg,
1
reaction treated as for A1L. Yield: 1.7 g, 65%. H NMR
d/ppm: 8.42 (3H m Anth), 8.06 (5H m Anth), 7.84 (1H d
[3JH–H 7.3 Hz] CH–Anth), 7.49 (8H m Anth), 7.28 (3H m
Anth + CH–Ph + Ph), 6.87 (1H dd Ph), 6.53 (1H d Ph).
1
2.4 mmol) as for A3L. Yield: 800 mg, 71%. H NMR d/
ppm: 8.54 (1H s 10-Anth), 8.05 (2H m Anth), 7.90 (2H m
3
Anth), 7.73 (1H d ), 7.60 (1H d JH–H 16 Hz), 7.49 (4H
8.2.2. (2-(2,5-Dibromophenyl)-2-hydroxyethyl)anthracene
THF–borane complex (from sodium borohydride
(1.07 mmol) and iodine (0.482 mmol) in THF) was pre-
pared as for A2L and added to (2-(2,5-dibromophenyl)eth-
enyl) anthracene (1 g, 2.3 mmol). The reaction and
subsequent oxidation with alkaline hydrogen peroxide
was performed as for A2L. Yield: 446 mg, 44% – mixture
of isomers. Major by-product – starting olefin, 300 mg
m Anth + Ph), 7.34 (1H s Ph), 7.26 (1 H dd Ph), 7.13
(1H d JH–H 16 Hz).
3
8.3.2. 9-(3-(2,5-Dibromophenyl)-1-hydroxypropyl)anthracene
9-(3-(2,5-Dibromophenyl)prop-2-enoneyl)anthracene
(800 mg, 1.7 mmol) was reduced to the anthracenyl alcohol
with sodium borohydride (258.5 mg, 6.8 mmol) using a
method analogous to that used for 9-(3-(4-bromophenyl)-
1-hydroxypropyl)anthracene. Yield: 779 mg, 97%. 1H
NMR d/ppm: 8.52 (1H s br OH), 8.30 (1H s 10-Anth), 7.94
(2H m Anth), 7.45 (4H m Anth), 7.30 (2H m Anth), 7.12
(1H m), 6.12 (1H m), 2.97 (1H m), 2.62 (3H m), 2.30 (1H m).
1
recovered. H NMR d/ppm: 8.73 (1H br s OH), 8.42 (1H
s 10-Anth), 8.00 (2H d Anth), 7.45 (8H m Anth + Ph),
6.6 (1H dd Ph), 4.1–3.4 (2 · 3H m mixture of isomers of
linker protons). Mass, m/z: 456 (M+), 440 (–O), 376/378
(M+ ꢀ 79Br/81Br), 278 (M+ ꢀ OH, Br).
8.3.3. 9-(3-(2,5-Bromophenyl)propyl)anthracene
8.2.3. (2-(2,5-Dibromophenyl)ethyl)anthracene
9-(3-(4-Bromophenyl)-1-hydroxypropyl)anthracene
(779 mg, 1.66 mmol) was reduced to the propyl derivative
using freshly prepared TMSI (10 mmol) as for A3L. Yield:
754 mg, Quantitative. 1H NMR d/ppm: 8.33 (1H s 10-
Anth), 8.20 (2H d Anth), 7.99 (2H d Anth), 7.48 (6H m
Anth + Ph), 7.19 (1H m Ph), 3.66 (2H t AnthCH2), 2.96
(2H t PhCH2), 2.13 (2H m R–CH2–R0). Mass, m/z: 454
(M+), 191 (Anth–Me).
(2-(2,5-Dibromophenyl)-2-hydroxyethyl)anthracene
(0.446 mg, 1 mmol) was treated with freshly prepared
TMSI (appox. 6 mmol) in acetonitrile and worked up as
for A2L. Silica column chromatography (DCM:hexane
10:90) yielded the desired product. Yield: 172 mg, 40%.
1H NMR d/ppm: 8.38 (2H d Anth), 8.33 (1H s Anth),
8.03 (2H d Anth), 7.48 (6H m Anth + Ph), 7.21 (1H m
Ph), 3.88 (2H m Anth–CH2), 3.16 (2H m Ph–CH2).
(2-(2,5-Dibromophenyl)ethyl)anthracene (172 mg, 0.4
mmol) was coupled with TMSA (0.12 ml, 0.88 mmol) via
a Sonogashira reaction as for A0L. Silica column chroma-
tography (DCM:hexane, 10:90) yielded the desired bis-
TMS protected product and a large (approx. 30%) amount
9-(2-(2,5-Trimethylsilylethynylphenyl)propyl)anthracene
was prepared from 9-(2-(2,5-bromophenyl)propyl)anthra-
cene (726.7 mg, 1.6 mmol) and TMSA (0.51 ml,
3.65 mmol) using a Heck coupling reaction modified from
1
that used for A0L. H NMR d/ppm: 8.35 (1H s 10-Anth),
8.22 (2H d Anth), 8.02 (2H d Anth), 7.48 (6H m
Anth + Ph), 7.20 (1H m Ph), 3.69 (2H t AnthCH2), 3.01
(2H m PhCH2), 2.19 (2H m R–CH2–R0), 0.31 (18H m
TMS). Mass, m/z: 488 (M+), 473 (–Me), 415 (–TMS),
400 (–TMS –Me), 191 (Anth–Me). The protecting groups
were then removed using potassium carbonate as for 1,4-
diethynylbenzene to yield A3T. 1H NMR d/ppm: 8.34
(1H s 10-Anth), 8.21 (2H d Anth), 8.02 (2H d Anth),
7.48 (6H m Anth + Ph), 7.32 (1H m Ph), 3.70 (2H t Ant-
hCH2), 3.25 (1H s CCH), 3.16 (1H s CCH), 3.02 (2H t
PhCH2), 2.19 (2H m R–CH2–R0). 13C NMR d/ppm:
140.0, 129.8, 128.1, 127.6, 127.4, 127.3, 126.8, 124.8,
124.7, 124.4, 121.0, 120.7, 120.0, 119.6, 117.7, 117.5, 78.5,
1
of monosubstituted product. H NMR d/ppm: 8.41 (2H d
Anth), 8.38 (1H s 10-Anth), 8.01 (2H d Anth), 7.51 (6H m
Anth + Ph), 7.32 (2H m Anth), 3.91 (2H m j-CH2), 3.23
(2H m i-CH2) 0.29 (18 H s TMS). Mass, m/z: 474 (M+),
459 (–Me), 401 (–TMS), 386 (–TMS, –Me), 191 (Anth–
Me).
This was then deprotected with potassium carbonate as
for A0L. Combined yield for Sonogashira and deprotection
steps and formation of A2T 92.4 mg, 71% 1H NMR d/ppm.
8.44 (1H s 10-Anth), 8.40 (2H d 4-Anth), 8.03 (2H d 1-
Anth), 7.50 (6H m 2,3-Anth + d,e), 7.35 (1H m g), 3.91
(2H m j) 3.48 (1H s a) 2.24 (2H m i), 2.23 (1H s a0). 13C

I. Cade et al. / Journal of Organometallic Chemistry 691 (2006) 1389–1401
1401
77.8, 77.0, 74.0, 30.0, 26.9, 22.8. Mass, m/z: 344 (M+), 191
Appendix A. Supplementary data
(Anth–Me). IR/cmꢀ1: 3297.9 m(C–H), 2107.0 m(C„CH).
UV/nm: DCM, 391 (0.410), 371 (0.431), 275 (0.910), 251,
(2.720). Acc. Mass. 344.155965 (Calc. 344.156501, C27H20).
Crystal data for A1L. C24H16, M = 304.37, monoclinic,
Supplementary data associated with this article can be
found, in the online version, at doi:10.1016/j.jorganchem.
2005.12.024.
˚
˚
P21/n (no. 14), a = 14.7618(14) A, b = 6.0866(5) A, c =
3
˚
˚
37.489(3) A, b = 100.148(7)ꢁ, V = 3315.6(5) A , Z = 8
(two independent molecules), Dc = 1.219 g cmꢀ3, l(Cu
Ka) = 0.523 mmꢀ1, T = 293 K, yellow needles; 4910 inde-
pendent measured reflections, F2 refinement, R1 = 0.062,
wR2 = 0.140 for 3100 independent observed reflections
[|Fo| > 4r(|Fo|), 2hmax = 120ꢁ], 434 parameters. CCDC
292095.
References
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˚
˚
P21 (no. 4), a = 5.5422(13) A, b = 12.995(2) A, c =
3
˚
˚
25.041(4) A, b = 93.09(2)ꢁ, V = 1800.9(6) A , Z = 4 (two
independent molecules), Dc = 1.182 g cmꢀ3, l(Mo Ka) =
0.067 mmꢀ1, T = 203 K, yellow hexagonal needles; 3336
independent measured reflections, F2 refinement, R1 =
0.052, wR2 = 0.115 for 2195 independent observed
reflections [|Fo| > 4r(|Fo|), 2hmax = 50 ꢁ], 460 parameters.
The absolute structure of A3L could not determined
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use of the Flack parameter [x+ = ꢀ9.99(999), xꢀ = +
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Crystal data for A2*L[Ru], M = 1210.63, monoclinic,
˚
˚
C2/c (no. 15), a = 24.3005(10) A, b = 9.8753(7) A, c =
3
˚
˚
51.476(3) A, b = 101.716(4)ꢁ, V = 12095.6(12) A , Z = 8,
Dc = 1.330 g cmꢀ3, l(Cu Ka) = 3.833 mmꢀ1, T = 293 K,
orange platy needles; 8329 independent measured reflec-
tions, F2 refinement, R1 = 0.052, wR2 = 0.122 for 6518
independent observed absorption corrected reflections
[|Fo| > 4r(|Fo|), 2hmax = 120ꢁ], 625 parameters. CCDC
292096.
(b) A.M. McDonagh, I.R. Whittall, M.G. Humphrey, B.W. Skelton,
A.H. White, J. Organomet. Chem. 519 (1996) 229;
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Crystal data for A1T. C26H16 Æ 0.5CH2Cl2, M = 370.85,
˚
monoclinic, C2/c (no. 15), a = 25.081(4) A, b =
[9] A.S.B. Prasad, J.V.B. Kanth, M. Presamy, Tetrahedron 48 (22)
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(1987) 3817.
˚
˚
8.7598(19) A, c = 19.273(3) A, b = 113.636(12)ꢁ, V =
3879.1(12) A , Z = 8, Dc = 1.270 g cmꢀ3, l(Cu Ka) = 1.780
3
˚
mmꢀ1, T = 293 K, yellow needles; 2867 independent mea-
sured reflections, F2 refinement, R1 = 0.050, wR2 = 0.142
for 2318 independent observed absorption corrected reflec-
tions [|Fo| > 4r(|Fo|), 2hmax = 120ꢁ], 263 parameters. CCDC
292098.
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Acknowledgements
[16] Y. Shimura, T. Kawai, T. Minegishi, Synthesis (1993) 43.
We wish to thank the EPSRC for a studentship for I.C.