New stable, isolable triarylmethyl based dyes absorbing in the near infrared

Article abstract of DOI:10.1016/j.jorganchem.2006.02.017

A series of new intensely coloured multicharged methylium compounds containing the 4-[2-ferrocenylethenyl]phenyl group and with significant electronic absorption in the near infrared have been prepared via acidification of the tertiary carbinols obtained by reaction of 4-[FcCH{double bond, long}CH]C₆H₄Li with diethyl isophthalate, diethyl terephthalate, diethyl phthalate or the triethyl ester of 1,3,5-benzene carboxylic acid. Even more stable dyes were prepared from two new triarylmethanol derivatives containing 2,6-dimethoxy-4-[2-(ferrocenyl)ethenyl]phenyl or 2,6-dimethoxy-4-[2-[4-(dimethylamino)phenyl]ethenyl]phenyl groups which were prepared by reaction of 4-[FcCH{double bond, long}CH]-2,6-MeO₂C₆H₂Li or 4-[4-Me₂NC₆H₄CH{double bond, long}CH]-2,6-MeO₂C₆H₂Li (Fc = ferrocenyl) with diethyl carbonate. These carbinols on treatment with acid deposit dark-purple crystals which have been isolated and characterised spectroscopically. They absorb in the near infrared and, whereas their solutions begin to decolourise only after several days, they display long-term stability to air and moisture in the solid state.

Full text of DOI:10.1016/j.jorganchem.2006.02.017

Journal of Organometallic Chemistry 691 (2006) 2785–2792
www.elsevier.com/locate/jorganchem
New stable, isolable triarylmethyl based dyes absorbing
in the near infrared
*
ˇ
Carolina Villalonga-Barber, Barry R. Steele , Veronika Kovac,
Maria Micha-Screttas, Constantinos G. Screttas
Institute of Organic and Pharmaceutical Chemistry, National Hellenic Research Foundation, Vas. Constantinou 48, Athens 116 35, Greece
Received 10 January 2006; received in revised form 10 February 2006; accepted 15 February 2006
Available online 6 March 2006
Abstract
A series of new intensely coloured multicharged methylium compounds containing the 4-[2-ferrocenylethenyl]phenyl group and with
significant electronic absorption in the near infrared have been prepared via acidification of the tertiary carbinols obtained by reaction of
4-[FcCH@CH]C6H4Li with diethyl isophthalate, diethyl terephthalate, diethyl phthalate or the triethyl ester of 1,3,5-benzene carboxylic
acid. Even more stable dyes were prepared from two new triarylmethanol derivatives containing 2,6-dimethoxy-4-[2-(ferrocenyl)-
ethenyl]phenyl or 2,6-dimethoxy-4-[2-[4-(dimethylamino)phenyl]ethenyl]phenyl groups which were prepared by reaction of 4-
[FcCH@CH]-2,6-MeO2C6H2Li or 4-[4-Me2NC6H4CH@CH]-2,6-MeO2C6H2Li (Fc = ferrocenyl) with diethyl carbonate. These carbinols
on treatment with acid deposit dark-purple crystals which have been isolated and characterised spectroscopically. They absorb in the
near infrared and, whereas their solutions begin to decolourise only after several days, they display long-term stability to air and moisture
in the solid state.
ꢀ 2006 Elsevier B.V. All rights reserved.
Keywords: Near infrared; Carbenium ion; Ferrocenyl; Stilbene
1. Introduction
gated organic chromophores with strong donor and
acceptor substituents which allows the possibility of
intramolecular charge transfer [4].
Acceptor substituted ferrocenes provide a building-
block for the synthesis of organometallic NIR dyes and
The present strong scientific and commercial interest in
near-infrared (NIR) absorbing dyes (kmax > 700 nm) arises
from their large range of potential applications in optical
imaging systems, infrared photography, optical lasers, bio-
logical probes, etc. [1,2]. Particularly significant is that bio-
logical fluids and tissues are relatively transparent in the
region from ca. 700 to 1100 nm and, for this reason, NIR
dyes have also attained special interest for their potential
applications in clinical chemistry and in photodynamic
tumour therapy [3].
Huckel calculations have shown that increasing the accep-
¨
tor strength gives rise to large bathochromic shifts due to a
considerable lowering of the already low-lying MLCT tran-
sition [5]. The optimal structural arrangement allows the
EWG to experience the electron releasing effect of the ferr-
ocenyl group [5a], and this is usually achieved through a
chain of sp2 hybridized carbon atoms [6] where p-delocal-
ization effects are obviously responsible for the transfer
of electron density.
A variety of electron-accepting groups have been
employed so far. These include conventional EWG’s, e.g.,
ANO2, ACN, ACH@O, ACO2CH3 [7], as well as other,
rather novel electron-withdrawing functionalities. Since
Dyes for applications in the NIR region require small
differences in the energy between the HOMO and LUMO.
This situation can be attained by end-capping of conju-
*
Corresponding author. Tel.: +30 2107273873; fax: +30 2107273877.
E-mail address: bsteele@eie.gr (B.R. Steele).
0022-328X/$ - see front matter ꢀ 2006 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2006.02.017

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C. Villalonga-Barber et al. / Journal of Organometallic Chemistry 691 (2006) 2785–2792
carbocations are the strongest known acceptor groups, and
following our previous experience in non-linear optical
materials [8] and our recent interest in NIR dyes [9], we
set out to asses the accumulative effect of multicharged car-
benium ion centres on the NIR properties of certain stil-
bene derivatives and to examine them in the context of
other recent reports of NIR triphenylmethane dyes by
Sengupta [10] and Meier [11].
UV–Vis spectra were recorded both for the carbinols as
well as for the corresponding triarylmethyl dyes generated
by dissolving the carbinols in chloroform containing triflu-
oroacetic acid (TFA). These carbocations could also be
generated by addition of 60% aq. HPF6, as indicated by
the intensely coloured solutions obtained (dark blue for
2a–c, dark red for 2d and 2e). In contrast to analogous
compounds [12], isolation of the above dyes could not be
achieved because during aqueous work-up the dyes rapidly
revert to their corresponding carbinols. Similar behaviour
has been observed by others for similar dyes [13]. Also,
compared to the analogous dyes 3a [10a] and 3b [9], the
dye solutions reported above are highly unstable. Only
minutes after preparation, the NIR band decreases in
intensity suggesting the solutions to be moisture
sensitive.
The electronic spectra of the dyes (see Table 1) exhibit
additional bands in the visible region presumably arising
from charge transfer (CT) as well as metal-to-ligand charge
transfer (MLCT) [14]. Also a small pH dependency was
observed so that, when the acid concentration was increased,
the NIR band gradually decreased and virtually vanished at
high acid concentrations (except for compounds 2d and 2e
where the opposite occurred). This is likely to be due to the
increasing protonation of the iron atoms of the ferrocenyl
2. Results and discussion
2.1. Preparation of bis and tri{4-[2(E)-
(ferrocenyl)ethenyl]phenylhydroxymethyl}benzenes
The synthesis of the new ferrocene derivatives involved
the use of the stilbenyllithium derived from the readily
accessible bromide 1 through a halogen–metal interchange
reaction [9]. Reaction of the in situ generated stilbenylli-
thium with the appropriate substrate gave carbinols 2a–
2e (Scheme 1).
Addition to diethyl phthalate under the same conditions
gave lactol 2d as the sole product. Generation of carbinol
2e required forcing reaction conditions, i.e., use of a large
excess of the organolithium reagent and heating the reac-
tion mixture at reflux for a week (Scheme 1).
Scheme 1. (i) nBuLi, THF, À78 to À65 ꢁC, 1 h then di or triester, THF, À78 ꢁC to r.t., 20 h; (ii) nBuLi, Et2O, 0 ꢁC to r.t, 1 h then diester, Et2O, 0–40 ꢁC,
1 week.

C. Villalonga-Barber et al. / Journal of Organometallic Chemistry 691 (2006) 2785–2792
2787
Table 1
Electronic spectra of carbinols 2a–2e and their carbenium ions
Entry
Compound
[dye] M
[TFA] M
kVis (loge)
kNIR (loge)
1
2
3
4
5
6
7
8
9
2a
2a
2a
2a
2a
2a
2b
2b
2b
2b
2b
2b
2b
2c
2c
2c
2c
2c
2c
2c
2d
2d
2d
2d
2d
2d
2e
2e
2e
2e
2e
2e
2e
2.80E-4
1.12E-4
1.12E-4
1.12E-4
1.12E-4
1.12E-4
2.80E-4
1.12E-1
1.12E-1
1.12E-1
5.60E-2
5.60E-2
5.60E-2
2.50E-4
1.00E-4
1.00E-4
2.5E-5
–
453 (3.75)
640 (4.47)
648 (4.35)
650 (4.19)
647 (4.40)
580 (3.40)
454 (3.70)
638 (4.50)
648 (4.56)
645 (4.45)
651 (4.32)
651 (4.40)
589 (4.51)
452 (3.69)
652 (2.47)
649 (3.60)
585 (3.57)
596 (4.46)
602 (4.04)
586 (4.50)
453 (3.59)
523 (4.25)
525 (4.29)
538 (4.28)
542 (4.28)
530 (4.29)
453 (3.55)
3.11E-1
5.16E-1
7.78E-1
1.29
2.58
–
3.11E-1
4.15E-1
5.16E-1
7.78E-1
1.29
2.58
–
3.11E-1
5.16E-1
1.29
2.58
6.49
7.74
–
3.11E-1
5.16E-1
7.78E-1
1.29
5.16
–
3.11E-1
5.16E-1
7.78E-1
1.29
2.58
5.16
1100 (4.25)
1100 (4.10)
1100 (3.85)
1037 (3.85)
1100 (3.94)
1100 (4.28)
1100 (4.24)
1100 (4.18)
1100 (3.95)
1100 (3.97)
925 (3.74)
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
1100 (4.15)
946 (3.69)
914 (3.64)
894 (3.66)
892 (3.71)
848 (3.70)
1.00E-4
2.5E-5
1.00E-4
4.50E-4
1.81E-4
1.81E-4
1.81E-4
1.81E-4
1.81E-4
3.40E-4
1.36E-4
1.36E-4
1.36E-4
1.36E-4
1.36E-4
1.36E-4
889 (3.81)
895 (4.08)
903 (4.07)
904 (4.09)
926 (4.08)
911 (3.00)
931 (3.20)
945 (3.26)
9.41 (3.37)
939 (3.44)
927 (3.46)
659 (3.07)
659 (3.10)
661 (3.20)
653 (3.27)
groups [15], which results in a diminishing probability for
MLCT [9]. Similar behaviour is found for the related triaryl
carbenium salt, 4a [10b], although a smaller excess of acid is
required there for changes in the electronic spectra, indicat-
ing that the basicity of an N,N-dimethylaniline is greater
than that of the ferrocenyl group. The anisyl group, like
the ferrocenyl group, also induces a weak pH-dependency
on the electronic absorption of carbocation 4b [16].
ing around the carbocationic centres preventing the cations
from becoming planar and therefore making delocalisation
of the charge more difficult.
2.2. Preparation of tris 4-susbstituted-2,6-
(dimethoxyphenyl)methanols
We reasoned that the introduction of some bulkiness
around the carbocationic centre would prevent the nucleo-
philic attack of water molecules and would therefore result
in more stable carbenium ions. It was also thought that the
substitution of the ortho positions of the triaryl carbenium
core with strong electron donor groups would, through res-
onance, stabilize the carbocation centre.
X
Fc
R
R
-
X-
CF3CO2
R
R
It is known that ortho methoxy groups in phenyl deriv-
atives give unusual physical and chemical properties to the
derivatives due to the steric and electronic effects of the
substituents and Wada [17] has demonstrated that the
number of methoxy substituents on phenyl groups influ-
ences the stability and reactivity of triphenylcarbenium
salts while the greater basicity of tris-2,6-dimethoxyphenyl-
methanol compared to that of triphenylmethanol has been
known for some time [18].
R
R
Fc
Fc
X
X
-
4a X = NMe2, R = Me
4b X= OMe, R = H
3a R = Me, X = BF4
3b R= H, X = CF3CO2
-
It is of interest to note the lower wavelength and lower
intensity of the NIR band for carbocations derived from
2d and 2e compared to 2a–c. This might be due to crowd-

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C. Villalonga-Barber et al. / Journal of Organometallic Chemistry 691 (2006) 2785–2792
Table 2
Considering this stability factor, we prepared ferrocene
Electronic spectra of carbinol 6a and carbenium ion 7a
derivative 6a and the analogue 6b for comparison with
the triarylmethanol derivatives that we had synthesised
previously [19]. The synthetic routes are similar to the prep-
aration of derivatives 2a–2e. Thus ortho-directed lithiation
of stilbenes 5a and 5b by n-butyllithium followed by addi-
tion of diethyl carbonate gave triarylmethanols 6a and 6b,
respectively (Scheme 2).
Stilbene derivatives 5a and 5b were prepared through
Horner–Emmons procedures by condensing, respectively,
ferrocenecarboxaldehyde and p-dimethylaminobenzalde-
hyde with diethyl 3,5-dimethoxyphenylphosphonate. The
latter was prepared from 3,5-dimethoxybenzylalcohol fol-
lowing the procedure described by Marder [20].
Carbinols 6a and 6b reacted with a slight excess of 60%
aqueous hexafluorophosphoric acid to give the carbenium
salts 7a and 7b, respectively, which could be isolated as
dark blue crystals which were stable to air and moisture.
The electronic spectrum of 7a was recorded in chloroform,
thus allowing comparison with those reported above, but
7b was insoluble in this solvent and so the spectrum was
recorded in acetonitrile.
Dye 7a exhibits strong additional bands in the visible
and in the NIR region compared to carbinol 6a. A similar
slight pH dependent behaviour was found to that of dyes
derived form carbinols 2a–2e, (Table 2) where the NIR
band virtually disappears at very high acid concentrations
(entry 7, Table 2)
It is worth mentioning that, one week after the prepara-
tion of the samples for UV measurements, some changes
were observed. The solution of 6a in chloroform in the
absence of acid (entry 1, Table 1) had turned from orange
to dark blue and its electronic spectrum now resembled
that of the carbenium salt 7a, with an absorption in the
NIR region (kmax = 904 nm). This suggests the facile for-
mation of the carbenium ion 7a from the carbinol even at
neutral conditions, resembling behaviour already observed
for tris(2,6-dimethoxyphenyl)methanol [17]. On the other
hand, the solutions corresponding to entries 2–7 of Table
2 had all lost their colour intensity and the NIR band
had disappeared. Their UV spectra were all similar but
did not resemble that of the carbinol 6a. A possibility could
Entry
Compound
[dye] M
[TFA] M
kVis (loge)
kNIR (loge)
1
2
4
5
6
7
8
6a
6a
6a
6a
6a
6a
7a
3.70E-4
3.70E-5
3.70E-5
3.70E-5
3.70E-5
3.70E-5
8.30E-5
–
452 (3.59)
643 (4.18)
635 (4.25)
620 (4.35)
622 (4.36)
645 (4.35)
638 (4.05)
5.19E-2
2.59E-1
1.29
6.49
11.7
–
914 (4.29)
920 (4.35)
950 (4.15)
926 (3.86)
–
900 (4.17)
be that the carbenium salt is reduced to the corresponding
triarylmethane, a reaction known to be possible in solvents
such as alcohols, diethyl ether or tetrahydrofuran [17].
Although this is still to be confirmed for our compound,
it might be plausible due to the small traces (0.6–1%) of
ethanol present in the HPLC grade chloroform used for
our dilutions. An alternative possibility is that the changes
are the result of photooxidation which is known to occur
for ferrocene derivatives in halocarbon solvents [21]. The
solution of 7a in chloroform was relatively more stable
and after a week the electronic spectrum was similar to that
recorded initially (kmax = 907 nm, loge = 4.10). However,
after a longer period of time (ca. 5 months) the spectra
again resemble those of week-old samples for entries 2–7
and presumably the reasons for this are similar to those
mentioned above.
Dye 7b also exhibited a band in the NIR region, but this
spectrum could not be compared to that of the carbinol 6b
from which it is derived since the carbocation forms readily
as indicated by the electronic spectrum with a characteristic
band at 845 nm (in acetonitrile). This band has a small
molar extinction coefficient (loge = 2.31) indicating a low
concentration of the carbocation in the fresh solution of
6b. As time progresses, however (just a few hours), light
yellow chloroform solutions of 6b turn deep blue and the
NIR band goes off scale, suggesting the facile formation
of the carbenium ion 7b at neutral conditions. The acetoni-
trile solution was more stable and no colour change was
appreciable to the eye after a few hours, although the
NIR band had slightly increased in intensity (loge = 2.46).
The absorption spectra of the dye show strong pH depen-
Scheme 2. (i) nBuLi, Et2O, 0 ꢁC to r.t, 20 h then diethyl carbonate, Et2O, 0–40 ꢁC, 48 h. (ii) HPF6, EtOH.

C. Villalonga-Barber et al. / Journal of Organometallic Chemistry 691 (2006) 2785–2792
2789
Table 3
Sodium hydride (60% in mineral oil) was washed with
dry hexane before use. The starting material (E)-bromosty-
rylferrocene (1) was synthesized as previously described [9].
Electronic spectra of carbinol 6b and carbenium ion 7b (in acetonitrile)
Entry
Compound
[dye] M
[TFA] M
kvis (loge)
kNIR (loge)
1
2
3
4
5
6
7
6b
6b
6b
6b
6b
6b
7b
4.10E-4
9.10E-5
4.10E-5
4.10E-5
4.10E-5
4.10E-5
4.80E-5
–
393 (3.81)
845 (2.31)
893 (4.48)
811 (4.63)
798 (4.46)
675 (4.48)
6.50E-3
1.30E-2
5.19E-2
1.29
6.49
–
3.2. 1,3-bis{4-[2(E)-(ferrocenyl)ethenyl]phenylhydroxy-
methyl}benzene (2a)
543 (3.86)
563 (4.02)
571 (4.19)
660 (4.48)
–
A solution of 1 (1.7 g, 4.6 mmol) in tetrahydrofuran
(30 mL) was cooled to À78 ꢁC by means of a liquid nitro-
gen–acetone bath. Rapid addition of n-butyllithium
(2.3 mL, 4.3 mmol; 1.87 M in methylcyclohexane) caused
the immediate appearance of a precipitate. The mixture
was stirred and warmed slowly up to À65 ꢁC. After 1 h
the mixture was re-cooled to À78 ꢁC and a solution of
diethyl isophthalate (171 mg, 0.77 mmol) in tetrahydrofu-
ran (3 mL) was added. Cooling was discontinued and the
resulting solution was left stirred overnight. NH4Cl (sat.
solution) (15 mL) was added and the solution concen-
trated. Dichloromethane (20 mL) was added and the
phases separated. After extraction of the aqueous layer
with two other portions of dichloromethane (2 · 20 mL),
the organic phases were collected and evaporated to dry-
ness under reduced pressure to afford an orange solid.
Recrystallization from chloroform and hexane afforded
carbinol 2a as an orange-red solid (877 mg, 88%). m.p.:
270 ꢁC (dec.). 1H NMR (CDCl3): 7.50–7.10 (m, 4H,
ArAH · 4), 7.32 (d, J 8.0, 8H, ArAH · 8), 7.20 (d, J 8.0,
8H, ArAH · 8), 6.85 (d, J 15.0, 4H, CH@ ·4), 6.65 (d, J
15.0, 4H, CH@ · 4), 4.48 (s, 8H, FcAH · 8), 4.30 (s, 8H,
FcAH · 8), 4.15 (s, 20H, Cp · 4) and 2.71 (s, 2H,
OH · 2). 13C NMR (CDCl3): 146.3, 145.3, 136.7, 128.1,
127.5, 127.4, 127.2, 126.7, 125.7, 125.4, 83.9 (C, quat.),
81.8 (C, quat.), 69.6 (Cp), 69.4 (FcACH) and 67.0
(FcACH). UV–Vis (CHCl3) kmax(loge) 453 nm (3.75). MS
(ESI) m/z (%): 1284.1 ([M+H]+, 10%), 1283.1 (M+, 10),
641.8 (30), 344.1 (90) and 287.9 (100). Calc. for
C80H66Fe4O2: C, 74.91; H, 5.19. Found: C, 74.99; H,
5.15%.
833 (4.54)
dent behaviour similarly to that of 4a [10b]. At low acid
concentrations the NIR band was the predominant one.
In strongly acidic solution, however, this band disappeared
and a lower wavelength band became the major one (Table
3). This has been observed for analogous systems and can
be attributed to the formation of the N-protonated dye
7bH+ [10b].
The solutions corresponding to entries 2 and 7 do not
experience a very substantial change over time. The NIR
band loses intensity and also blue shifts slightly (kmax = 888
loge = 4.46 after one week and kmax = 843 loge = 4.06 after
5 months for solution in entry 2 and kmax = 792 loge = 4.24
after 5 months for solution in entry 4). This indicates that
the specific samples were relatively stable especially com-
pared to the corresponding ferrocenyl derivative in which,
as mentioned previously, the solvent may be implicated in
the appearance of secondary reaction products [17,21].
3. Experimental
3.1. General
All reactions requiring dry or inert conditions were car-
ried out in flame dried equipment under an atmosphere of
argon. Solvents were dried under argon by conventional
methods. Reactions were monitored by TLC using com-
mercially available Merck Kieselgel 60 F254. After aqueous
work-up of reactions mixtures, organic solutions were rou-
tinely dried over anhydrous sodium sulphate. Column
chromatography was carried out on Kieselgel 60 (particle
size 40–63 lm) as supplied by Merck. NMR spectra were
recorded in solutions of CDCl3 unless stated otherwise
3.3. 1,4-bis{4-[2(E)-(ferrocenyl)ethenyl]phenylhydroxy-
methyl}benzene (2b)
Prepared as above from 1 (1.8 g, 4.9 mmol), n-butylli-
thium (2.4 mL, 4.5 mmol; 1.87 M in methylcyclohexane)
and diethyl terephthalate (180 mg, 0.80 mmol) to give the
title compound as an orange-red solid after recrystalliza-
tion from chloroform and hexane (940 mg, 91%). m.p.:
250 ꢁC (dec.). 1H NMR, (THF-d8): 7.38 (d, J 8.5, 8H,
ArAH · 8), 7.26 (d, J 8.5, 12H, ArAH · 12), 6.90 (d, J
16.0, 4H, CH@ ·4), 6.71 (d, J 16.0, 4H, CH@ ·4), 5.41
(s, 2H, OH · 2), 4.46 (s, 8H, FcAH · 8), 4.22 (s, 8H,
FcAH · 8) and 4.07 (s, 20H, Cp · 4). 13C NMR (THF-
d8): 147.6, 147.4, 137.4, 129.1, 128.1, 127.5, 126.5, 125.7,
84.5 (C, quat.), 81.5 (C, quat.), 69.8 (Cp), 69.6 (FcACH)
and 67.6 (FcACH). UV–Vis (CHCl3) kmax(log e) 454 nm
(3.70). MS (ESI) m/z (%): 1283.8 ([M+H]+, 65%), 1282.1
(M+, 40), 642.3 (100), 641.4 (90) and 287.9 (60). Calc. for
on
a
Bruker AC 300 spectrometer operating at
300.13 MHz for 1H and 75.04 MHz for 13C. Chemical
shifts are reported in ppm relative to residual CHCl3 (dH
7.27) or to CDCl3 (dC, central line of triplet: 77.0). Cou-
pling constants (J) are given to the nearest 0.5 Hz. UV–
Vis spectra were recorded on a Hitachi Model U-2001.
Mass spectrometry was performed using a Finnigam MT
TSQ7000 with electrospray injection (ESI) and GC–MS
using a Varian Saturn 2000 with 30 m · 0.25 m DB5-MS
column. Elemental analyses were performed at the
National Hellenic Research Foundation using a Perkin–
Elmer PE2400 II analyser.
The solution of n-butyllithium in methylcyclohexane
was prepared by following the conventional procedure.

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C. Villalonga-Barber et al. / Journal of Organometallic Chemistry 691 (2006) 2785–2792
C80H66Fe4O2: C, 74.91; H, 5.19. Found: C, 74.82; H,
5.25%.
and allowed to warm up to r.t. during a period of 1 h. It
was then recooled to 0 ꢁC and a solution of diethyl phtha-
late (222 mg, 1.0 mmol) in diethyl ether (3 mL) was added.
Cooling was discontinued and the resulting solution was
warmed up to reflux temperature for one week. NH4Cl
(sat. solution) (15 mL) was added and the solution concen-
trated. Dichloromethane (20 mL) was added and the
phases separated. After extraction of the aqueous layer
with two other portions of dichloromethane (2 · 20 mL),
the organic phases were collected and evaporated to dry-
ness under reduced pressure to afford an orange solid.
Recrystallization from diethyl ether and hexane afforded
carbinol 2e as an orange-red amorphous solid (1.0 g,
3.4. 1,3,5-tri{4-[2(E)-(ferrocenyl)ethenyl]phenylhydroxy-
methyl}benzene (2c)
Prepared as above from 1 (2.25 g, 6.1 mmol), n-butylli-
thium, (4.3 mL, 5.7 mmol; 1.35 M in methylcyclohexane)
and triethyl ester 1,3,5-benzene tricarboxylic acid
(200 mg, 0.68 mmol) to give the title compound as an
orange-red solid after recrystallization from chloroform
and hexane (900 mg, 70%). m.p.: >300 ꢁC (dec.). 1H
NMR, (THF-d8): 7.38 (s, 3H, ArAH · 3), 7.27 (d, J 8.0,
12H, ArAH · 12), 7.16 (d, J 8.0, 12H, ArAH · 12), 6.90
(d, J 16.0, 6H, CH@ ·6), 6.71 (d, J 16.0, 6H, CH@ ·6),
5.40 (s, 3H, OH · 2), 4.46 (s, 12H, FcAH · 12), 4.23 (s,
12H, FcAH · 12) and 4.00 (s, 30H, Cp · 6). 13C NMR
(THF-d8): 147.9 (ArAC, quat.), 147.1 (ArAC, quat.),
137.1 (ArAC, quat.), 129.2 (CH), 127.3 (CH), 126.8
(CH), 125.6 (CH), 84.5 (C, quat.), 81.8 (C, quat.), 69.8
(Cp), 69.6 (FcACH) and 67.6 (FcACH). UV–Vis (CHCl3)
1
78%). H NMR (CDCl3): 7.60–7.00 (m, 4H, ArAH · 4),
7.37 (d, J 8.0, 8H, ArAH · 8), 7.12 (d, J 8.0, 8H,
ArAH · 8), 6.89 (d, J 15.0, 4H, CH@ ·4), 6.71 (d, J 15.0,
4H, CH@ ·4), 4.47 (s, 8H, FcAH · 4), 4.29 (s, 8H,
FcAH · 4) and 4.15 (s, 20H, Cp · 4). 13C NMR (CDCl3):
146.9 (ArAC, quat.), 144.4 (ArAC, quat.), 136.7 (ArAC,
quat.), 133.4 (CH), 128.2 (CH), 127.2 (CH), 126.0 (CH),
125.5 (CH), 125.3 (CH), 84.2 (C, quat.), 83.3 (C, quat.),
69.2 (Cp), 69.0 (FcACH) and 66.8 (FcACH). UV–Vis
(CHCl3) kmax(loge) 453 nm (3.55). MS (ESI) m/z (%):
1284.1 ([M+H]+, 30%), 1283.1 (M+, 20), 641.8 (50), 344.1
(80) and 287.9 (100). Calc. for C80H66Fe4O2: C, 74.91; H,
5.19. Found: C, 74.98; H, 5.17%.
k
max(loge) 453 nm (3.69). MS (ESI) m/z (%): 1885.4
([M+H]+, 60%), 1884.2 (M+, 50), 943.2 (100) and 942.4
(100). Calc. for C117H96Fe6O3: C, 74.55; H, 5.13. Found:
C, 74.64; H, 5.12%.
3.5. 1,3,3-tri{4-[2(E)-(ferrocenyl)ethenyl]phenyl}-1,3-
dihydro-isobenzofuran-1-ol (2d)
3.7. Diethyl 3,5-dimethoxyphenylphosphonate
Prepared as above from 1 (1.7 g, 4.6 mmol), n-butylli-
thium, (2.3 mL, 4.3 mmol; 1.87 M in methylcyclohexane)
and diethyl phthalate (171 mg, 0.77 mmol) to give the title
compound as an orange-red solid after recrystallization
from chloroform and hexane (755 mg, 98%). m.p.: 165 ꢁC
(dec.). 1H NMR, (CDCl3): 7.65–7.25 (m, 16H,
ArAH · 16), 6.87 (d, J 16.0, 3H, CH@ ·3), 6.67 (d, J
16.0, 3H, CH@ ·3), 4.47 (s, 6H, FcAH · 6), 4.29 (s, 6H,
FcAH · 6), 4.14 (s, 15H, Cp · 3) and 3.0 (s, 1H, OH).
13C NMR (CDCl3): 144.3 (ArAC, quat.), 143.3 (ArAC,
quat.), 142.9 (ArAC, quat.), 142.6 (ArAC, quat.), 140.9
(ArAC, quat.), 137.8 (ArAC, quat.), 137.2 (ArAC, quat.),
137.0 (ArAC, quat.), 129.2 (CH), 128.6 (CH), 128.0 (CH),
127.4 (CH), 127.3 (CH), 126.2 (CH), 125.6 (CH), 125.5
(CH), 123.8 (CH), 123.3 (CH), 107.8 (C, quat.), 92.7 (C,
quat.), 83.3 (Fc-C, quat.), 69.2 (Cp), 69.1 (FcACH) and
To a mixture of 3,5-dimethoxybenzylalcohol (17.4 g,
103 mmol) in triethyl phosphite (80 mL) was added iodine
(28.8 g, 113 mmol) at 0 ꢁC slowly. After stirring for 5 min
the mixture was heated to 150 ꢁC for 3 h. The excess tri-
ethyl phosphite was distilled out under vacuum. The
remaining liquid was purified by distillation under vacuum
to give the title compound as a clear oil (26.7 g, 89.5%). bp:
130–140 ꢁC/0.1 mbar. 1H NMR (CDCl3): 6.43 (s, 2H,
ArAH · 2), 6.43 (s, 1H, ArAH), 4.10–3.90 (m, 4H,
P(OCH2CH3)2) 3.74 (s, 6H, OMe · 2), 3.06 (d, JH–P 21.5,
2H, CH2AP) and 1.23 (t, J 7.0, 6H, Me · 2); 13C NMR
(CDCl3): 160.6 (ArAC, quat.), 133.4 (ArAC, quat., d,
JC–P 7.5), 107 (ArACH, d, JC–P 5.0), 98.9 (ArACH), 62.1
(P(OCH2CH3)2, d, JC–P 7.5), 55.1 (OMe), 33.8 (CH2AP,
d, JC–P 140) and 16.2 (Me); MS (EI) m/z (%): 288 (M+,
288%) and 273 (100).
66.8 (FcACH). UV–Vis (CHCl3)
kmax(loge) 453 nm
(3.59). MS (ESI) m/z (%): 995.5 ([M+H]+, 10%), 994.5
(M+, 15), 574.2 (50), 497.4 (20) and 287.9 (30). Calc. for
C62H50Fe3O2: C, 74.87; H, 5.07. Found: C, 74.91; H,
5.04%.
3.8. (E)-1-2-(ferrocenylethenyl)-3,5-dimethoxybenzene
(5a)
A solution of diethyl 3,5-dimethoxyphenylphosphonate
(11.8 g, 41.0 mmol) in tetrahydrofuran (50 mL) was added
to a suspension of sodium hydride (4.5 g, 112.2 mmol; 60%
in mineral oil) in tetrahydrofuran (20 mL) at r.t. The mix-
ture was allowed to stirred for 1 h before adding a solution
of ferrocenecarboxaldehyde (8.0 g, 37.4 mmol) in tetrahy-
drofuran (30 mL). After stirring the reaction mixture at
reflux temperature for 18 h, methanol was added and the
3.6. 1,2-bis{4-[2(E)-(ferrocenyl)ethenyl]phenylhydroxy-
methyl}benzene (2e)
n-Butyllithium (5.5 mL, 7.5 mmol; 1.35 M in methylcy-
clohexane) was added to a solution of 1 (2.9 g, 8.0 mmol)
in diethyl ether (40 mL) at 0 ꢁC. The mixture was stirred

C. Villalonga-Barber et al. / Journal of Organometallic Chemistry 691 (2006) 2785–2792
2791
solvent evaporated. The residue was redissolved into
dichloromethane (80 mL), washed with brine (50 mL),
dried and evaporated. The crude product was recrystallized
from isopropanol to give the title compound as an orange
125.6, 125.5, 103.7, 83.6 (C, quat.), 69.1 (Cp), 68.8
(FcACH), 66.6 (FcACH) and 56.4 (OMe). UV–Vis
(CHCl3) kmax(loge) 452 nm (3.59). MS (ESI) m/z (%):
1054.8 ([M+HÀOH]+, 80%), 1053.7 ([MÀOH]+, 100).
Calc. for C61H58Fe3O7: C, 68.43; H, 5.46. Found: C,
68.50; H, 5.44%.
1
solid (10.6 g, 81%). m.p.: 109A112 ꢁC. H NMR (CDCl3):
6.86 (d, J 16.0, 1H, CH@), 6.63 (d, J 16.0, 1H, CH@), 6.60
(d, J 2.0, 2H, ArAH · 2), 6.37 (t, J 2.0, 1H, ArAH), 4.46 (s,
2H, FcAH · 2), 4.29 (s, 2H, FcAH · 2), 4.15 (s, 5H, Cp)
and 3.84 (s, 6H, OMe · 2). 13C NMR (CDCl3): 160.9
(ArAC, quat.), 139.9 (ArAC, quat.), 127.5 (CH), 125.8
(CH), 103.8 (CH), 99.1 (CH), 82.9 (FcAC, quat.), 69.2
(Cp), 69.0 (FcACH), 66.9 (FcACH) and 55.3 (OMe). MS
(ESI) m/z (%): 348.1 (M+, 100).
3.11. Tris {4-[2-(E)-[4-(dimethylamino)phenyl]ethenyl]-
2,6-(dimethoxy)phenyl}methanol (6b)
Prepared as above from 5b (1.0 g, 3.5 mmol), n-butylli-
thium, (1.9 mL, 3.6 mmol; 1.88 M in methylcyclohexane),
and diethyl carbonate (106 lL, 0.875 mmol) to give the title
compound as a dark yellow solid after crystallization from
1
3.9. N,N-dimethyl-4-[(E)-2-(3,5-
dimethoxyphenyl)ethenyl] benzeneamine (5b)
diethyl ether (400 mg, 52%). m.p.: 165 ꢁC (dec). H NMR
(CDCl3): 7.40 (d, J 8.5, 6H, ArAH · 6), 6.98 (d, J 16.0,
3H, CH@ ·3), 6.84 (d, J 16.0, 3H, CH@ ·3), 6.71 (d, J
8.5, 6H, ArAH · 6), 6.64 (s, 6H, ArAH · 6), 3.53 (s,
18H, OMe · 6) and 2.98 (s, 18H, NMe2 · 3). 13C NMR
(CDCl3): 158.6 (ArAC, quat.), 149.8 (ArAC, quat.),
135.9, 127.5, 127.3, 125.8, 124.8, 112.4, 103.9, 77.2, 56.3
(OMe · 2) and 40.41 (NMe2). UV–Vis (CH3CN) kmax(log
e) 393 nm (3.81). MS (ESI) m/z (%): 860.0 ([M+HÀOH]+,
70%) and 858.9 ([MÀOH]+, 100). Calc. for C55H61N3O7:
C, 75.40; H, 7.02; N, 4.80. Found: C, 75.37; H, 7.06; N,
4.72%.
Prepared as above from 3,5-dimethoxyphenylphospho-
nate (10.0 g, 35.4 mmol), sodium hydride (3.8 g, 95 mmol;
60% in mineral oil) and 4-dimethylaminobenzaldehyde
(4.7 g, 31.5 mmol) to give the title compound as a dark yel-
low solid after recrystallization from isopropanol (6.0 g,
1
67.5%). m.p.: 82–84 ꢁC. H NMR (CDCl3): 7.44 (d, J 8.5,
2H, ArAH · 2), 7.06 (d, J 16.0, 1H, CH@), 6.83 (d, J
16.0, 1H, CH@), 6.73 (d, J 8.5, 2H, ArAH · 2), 6.67 (d,
J 2.0, 2H, ArAH · 2), 6.37 (t, J 2.0, 1H, ArAH), 3.85 (s,
6H, OMe · 2) and 3.00 (s, 6H, NMe2). 13C NMR (CDCl3):
160.8 (ArAC, quat.), 150.1 (ArAC, quat.), 140.1 (ArAC,
quat.), 129.3, 127.6, 125.3, 124.2, 112.3, 103.9, 99.1, 55.3
(OMe) and 40.4 (NMe2). MS (ESI) m/z (%): 284.1
([M+H]+, 20%), 283.1 (M+, 100) and 266 (50).
3.12. Tris{2,6-dimethoxy-4-[2-(E)-(ferrocenyl)ethenyl]-
phenyl}carbenium hexafluorophosphate (7a)
Hexafluorophosphoric acid (20 ll; 60% in water) was
added to a suspension of carbinol 6a (50 mg, 0.046 mmol)
in ethanol (1 mL) at room temperature. The mixture
became dark blue immediately. Diethyl ether was added
(1 mL) followed by hexane (1 mL) and the suspension
was filtered washed with hexane and dried under vacuum
to give the title compound as dark blue solid (37 mg,
3.10. Tris {2,6-dimethoxy-4-[2-(E)-(ferrocenyl)ethenyl]-
phenyl}methanol (6a)
n-Butyllithium (1.8 mL, 2.51 mmol; 1.40 M in methylcy-
clohexane) was added to a suspension of 5a (1.0 g,
2.87 mmol) in diethyl ether (150 mL) at 0 ꢁC. The mixture
was allowed to warm up to r.t. and stirred at that temper-
ature for 20 h. It was then recooled to 0 ꢁC and a solution
of triethyl carbonate (86 lL, 0.71 mmol) in diethyl ether
(1 mL) was added. Cooling was discontinued and the
resulting solution was warmed up to reflux temperature
over 48 h. NH4Cl (sat. solution) (10 mL) was added and
the solution concentrated. Dichloromethane (10 mL) was
added and the phases separated. After extraction of the
aqueous layer with two other portions of dichloromethane
(2 · 10 mL), the organic phases were collected and evapo-
rated to dryness under reduced pressure to afford an orange
oil. On treatment with diethyl ether a precipitate appeared
which was filtered and recrystallized from isopropyl alco-
hol to give the title compound as an orange-red solid
(300 mg, 40%). m.p.: 135–140 ꢁC (dec.). 1H NMR (CDCl3):
6.77 (d, J 16.5, 3H, CH@ ·3), 6.61 (d, J 16.5, 3H,
CH@ ·3), 6.61 (s, 6H, ArAH · 6), 4.44 (s, 6H, FcAH · 6),
4.27 (s, 6H, FcAH · 6), 4.15 (s, 15H, Cp · 3) and 3.56 (s,
18H, OMe · 6). 13C NMR (CDCl3): 158.6, 135.7, 126.6,
1
67%). H NMR (CD3CN): 7.40 (d, J 15.0, 3H, CH@ ·3),
6.66 (d, J 15.0, 3H, CH@ ·3), 6.61 (s, 6H, ArAH · 6),
4.85 (s, 6H, FcAH · 6), 4.72 (s, 6H, FcAH · 6), 4.37 (s,
15H, Cp · 3) and 3.56 (s, 18H, OMe · 6). 13C NMR
(CD3CN): 162.6 (ArAC, quat.), 149.5 (ArAC, quat.),
137.3 (CH), 126.8 (CH), 126.3 (ArAC, quat.), 103.3
(CH), 73.7 (CH), 72.6.1 (CH), 70.0 (CH) and 56.9
(OMe). UV–Vis (CHCl3) kmax(log e) 645 nm (4.35) and
900 nm (4.17). MS (ESI) m/z (%): 1054.8 ([M+HÀPF6]+,
80%) and 1053.7 ([MÀPF6]+, 100). Calc. for
C61H57F6Fe3O6P + H2O: C, 60.22; H, 4.89. Found: C,
60.55; H, 4.81%.
3.13. Tris{2,6-dimethoxy-4-[2-(E)-[4-(dimethylamino)-
phenyl]ethenyl]phenyl}carbenium hexafluorophosphate
(7b)
Prepared as above from hexafluorophosphoric acid
(50 ll; 60% in water) and carbinol 6b (100 mg, 0.11 mmol)
to give the title compound as dark blue solid (100 mg,

2792
C. Villalonga-Barber et al. / Journal of Organometallic Chemistry 691 (2006) 2785–2792
1
[3] R. Raghavachari (Ed.), Near-Infrared Applications in Biotechnology,
Practical Spectroscopy, vol. 25, Marcel Dekker Inc., 2001.
[4] H. Meier, Angew. Chem., Int. Ed. 44 (2005) 2482.
[5] (a) M.L.H. Green, S.R. Marder, M.E. Thompson, J.A. Brady, D.
Bloor, P.V. Kolinsky, R.J. Jones, Nature 330 (1987) 360;
(b) J.C. Calabrese, L.-T. Cheng, J.C. Green, S.R. Marder, W. Tam,
J. Am. Chem. Soc. 113 (1991) 7227;
(c) H.E. Bunting, M.L.H. Green, S.R. Marder, M.E. Thompson, D.
Bloor, P.V. Kolinsky, P.V. Jones, Polyhedron 11 (1992) 1489.
[6] (a) N.J. Long, Angew. Chem., Int. Ed. 34 (1995) 21;
(b) I. Ledoux, Synth. Metals 54 (1993) 123.
[7] K.M. Jayaprakash, P.C. Ray, I. Matsuoka, M.M. Bhadbhade, V.G.
Puranik, P.K. Das, H. Nishihara, A. Sarkar, Organometallics 18
(1999) 3851, and references therein.
[8] C. Arbez-Gindre, C.G. Screttas, C. Fiorini, C. Schmidt, J.-M. Nunzi,
Tetrahedron Lett. 40 (1999) 7413.
90%). H NMR (CD3CN): 7.80 (d, J 8.5, 6H, ArAH · 6),
7.63 (d, J 16.5, 3H, CH@ ·3), 7.52 (d, J 8.5, 6H,
ArAH · 6), 7.30 (d, J 16.5, 3H, CH@ ·3), 6.83 (s, 6H,
ArAH · 6), 3.62 (s, 18H, OMe · 6) and 3.23 (s, 18H,
NMe2 · 3). 13C NMR (CD3CN): 163.2 (ArAC, quat.),
149.9 (ArAC, quat.), 144.1 (ArAC, quat.), 138.2 (ArAC,
quat.), 134.3 (CH), 130.5 (CH), 130.2 (CH), 126.1 (ArAC,
quat.), 121.4 (CH), 104.1 (CH), 57.2 (OMe · 2) and 47.6
(NMe2). UV–Vis (CH3CN) kmax(log e) 833 nm (4.54). MS
(ESI) m/z (%): 859.8 ([M+HÀPF6]+, 60%) and
858.8 ([MÀPF6]+, 100). Calc. for C55H60F6N3O6P + H2O:
C, 64.63; H, 6.11; N, 4.11. Found: C, 64.81; H, 6.00; N,
4.05%.
[9] C. Arbez-Gindre, B.R. Steele, G.A. Heropoulos, C.G. Screttas, J.-E.
Communal, W.J. Blau, I. Ledoux-Rak, J. Organomet. Chem. 690
(2005) 1620.
3.14. Sample preparation for the pH dependent absorption
measurements
[10] (a) S. Sengupta, S.K. Sadhukhan, J. Mater. Chem. 10 (2000) 1997;
(b) S. Sengupta, S.K. Sadhukhan, J. Chem. Soc., Perkin Trans. 1 24
(2000) 4332;
(c) S. Sengupta, Tetrahedron Lett. 44 (2003) 307.
[11] H. Meier, S. Kim, Eur. J. Org. Chem. 6 (2001) 1163.
[12] A. Noak, A. Schro¨der, H. Hartmann, D. Rohde, L. Dunsch, Org.
Lett. 5 (2003) 2393.
[13] Similar behaviour is observed for dyes prepared by Sengupta (Ref.
[10a]) and Meier (Ref. [11]).
[14] S. Barlow, H.E. Bunting, C. Ringham, J.C. Green, G.U. Bublitz,
S.G. Boxer, J.W. Perry, S.R. Marder, J. Am. Chem. Soc. 121
(1999) 3715.
Stock solutions for the dyes (2.50E-4 M to 4.10E-4 M
see text) and TFA (51.9E-2 M or 1.29 M) were prepared
in CHCl3. The dye solutions were prepared by mixing 1
or 2 mL of the dye base solution with varying amounts
of the TFA solutions or with varying amounts of neat
TFA and the final volumes adjusted to 5 or 10 mL with
CHCl3.
Acknowledgements
[15] N.E. Watts, in: G. Wilkinson, F.G.A. Stone, E.N. Abel (Eds.),
Comprehensive Organometallic Chemistry, vol. 8, Pergamon, New
York, 1982, pp. 1019–1021.
[16] Unpublished work from our laboratory. Cf. similar results by Meier
(Ref. [4]).
[17] M. Wada, H. Mishima, T. Watanabe, S. Natsume, H. Konishi, S.
Hayase, T. Erabi, J. Chem. Soc., Chem. Commun. (1993) 1462.
[18] J.C. Martin, R.G. Smith, J. Am. Chem. Soc. 86 (1964) 2252.
[19] For an analogue of 6a see Ref. [9] and for an analogue of 6b see Ref.
[8].
A Marie Curie Intra-European Individual Fellowship to
C.V.-B. (contract No. MEIF-CT-2003-501082) and an
ENTER programme grant from the General Secretariat
for Research for Technology to V.K. are gratefully
acknowledged.
References
[20] S.J. Zheng, S. Barlow, T.C. Parker, S.R. Marder, Tetrahedron Lett.
44 (2003) 7989.
[21] P. Bergamini, S. DiMartino, A. Maldotti, S. Sostero, O. Traverso, J.
Organomet. Chem. 365 (1988) 341;
[1] J. Fabian, H. Nakazumi, M. Matsuoka, Chem. Rev. 92 (1992) 1197.
[2] S. Daehne, U. Resch-Genger, O.S. Wolfeibs (Eds.), Near-Infrared
Dyes for High Technology Applications, Kluwer Academic Publish-
ers, Dordrecht, 1998.
O. Traverso, F. Scandola, Inorg. Chim. Acta 4 (1970) 493.