Novel push-pull butadienes derived from 1,1-diaryl-2-propyn-1-ols and 1,1,1,5,5,5-hexafluoro-2,4-pentanedione: Synthesis, absorption spectra and solvatochromic behaviour

Article abstract of DOI:10.1016/j.dyepig.2010.03.028

Butadiene dyes were synthesized by the catalytic C-C coupling of 1,1-diaryl-2-propyn-1-ols with 1,1,1,5,5,5-hexafluoro-2,4-pentanedione. The reaction, which was promoted by the 16e^- (η³-allyl)-ruthenium(II) complex [Ru(η³-

Full text of DOI:10.1016/j.dyepig.2010.03.028

Dyes and Pigments 87 (2010) 209e217
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Dyes and Pigments
journal homepage: www.elsevier.com/locate/dyepig
Novel pushepull butadienes derived from 1,1-diaryl-2-propyn-1-ols
and 1,1,1,5,5,5-hexafluoro-2,4-pentanedione: Synthesis, absorption
spectra and solvatochromic behaviour
,
b
b
,
b
Javier Borge a, Victorio Cadierno b , Josefina Díez , Sergio E. García-Garrido , José Gimeno
*
*
a Departamento de Química Física y Analítica, Facultad de Química, Universidad de Oviedo, E-33071 Oviedo, Spain
b Departamento de Química Orgánica e Inorgánica, Instituto Universitario de Química Organometálica “Enrique Moles” (Unidad Asociada al CSIC),
Facultad de Química, Universidad de Oviedo, E-33071 Oviedo, Spain
a r t i c l e i n f o
a b s t r a c t
Article history:
Butadiene dyes were synthesized by the catalytic CeC coupling of 1,1-diaryl-2-propyn-1-ols with
1,1,1,5,5,5-hexafluoro-2,4-pentanedione. The reaction, which was promoted by the 16eꢀ 3-allyl)-
ruthenium(II) complex [Ru(
3-2-C3H4Me)(CO)(dppf)][SbF6], involved the MeyereSchuster rearrange-
ment of the aromatic alkynol and subsequent aldol-type condensation of the resulting enal with the
fluorinated -dicarbonyl compound. The absorption spectra of the dyes, as well as their solvatochromic
Received 3 February 2010
Received in revised form
25 March 2010
Accepted 29 March 2010
Available online 7 April 2010
(
h
h
b
behaviour, were studied; the structure of (4-C6H4OMe)2C]CHeCH]C(COCF3)2 was unambiguously
confirmed by means of single-crystal X-ray diffraction.
Keywords:
Butadiene dyes
Ó 2010 Elsevier Ltd. All rights reserved.
Solvatochromic behaviour
Homogeneous catalysis
MeyereSchuster rearrangement
Ruthenium
Trifluorometyl-ketones
1. Introduction
opposite end of the conjugated framework (R1/R2 substituents).
However, despite the potential applications of the resulting chro-
The synthesis of organofluorine compounds has attracted a great
deal of attention in recent years as the relatively small size and high
electronegativity of the fluorine atom often imparts unusual prop-
erties to organic molecules into which it is incorporated [1]. In
particular, useful effects have been noted when fluorine is included
mophores [6], studies in this direction have been scarce. Thus, to the
best of our knowledge, only the use of the 1-substituted-4,4-bis
(trifluoroacetyl)-1,3-butadiene dyes A and B (Fig. 1) for developing
light filters [7] and doped polymeric non-linear optical (NLO)
materials [8], respectively, has been described to date.
in photochromic [2] and biologically active molecules [3].
a,b-
Based on the ability of the 16-electron (h
3-allyl)-ruthenium(II)
Unsaturated trifluoromethyl-ketones R1R2C]C(R3)C(]O)CF3 are
organofluorine compounds that have been widely used as building
blocks in synthetic organic chemistry because of their enhanced
reactivity towards nucleophiles [4]. In contrast, little is known about
more extended conjugated dienone systems, i.e. R1R2C]CHCH]C
(R3)C(]O)CF3, mainly due to the lack of general synthetic
complex [Ru(h3-2-C3H4Me)(CO)(dppf)][SbF6] (1; dppf ¼ 1,10-bis
(diphenylphosphino)ferrocene) [9] to promote the Meyere
Schuster rearrangement of terminal propargylic alcohols into the
corresponding enals C [10], we recently described a straightforward
and general catalytic approach to conjugated dienones D starting
from readily available diaryl-substituted alkynols and enolizable
ketones (Scheme 1) [11]. This tandem isomerization/aldol
condensation process, which proceeds in a one-pot manner with
approaches [4,5]. Taking advantage of the p-electron delocalization
associated to the presence of a butadienic chain and the strong
accepting properties of the trifluoroacetyl group, this type of systems
could be suitable for the design of new pushepull compounds by
attachment of appropriate electron-donor functionalities at the
complete E-stereoselectivity, was also operative with b-diketones
allowing the high-yield preparation of a number of diene-dione
derivatives E structurally related to dyes AeB [11].
Pursuing our studies aimed at exploiting the utility of this
synthetic route, this paper concerns the preparation of a series of
pushepull 1,1-diaryl-4,4-bis(trifluoroacetyl)-1,3-butadiene dyes, such
as F in Fig. 2, by catalytic CeC coupling of 1,1-diaryl-2-propyn-1-ols
* Corresponding authors. Tel.: þ34 985 102 985; fax: þ34 985 103 446.
E-mail addresses: vcm@uniovi.es (V. Cadierno), garciagsergio@uniovi.es
(S.E. García-Garrido).
0143-7208/$ e see front matter Ó 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.dyepig.2010.03.028

210
J. Borge et al. / Dyes and Pigments 87 (2010) 209e217
Fig. 1. Structure of bis(trifluoroacetyl)-1,3-butadiene dyes A and B.
Fig. 2. Representative examples of the butadiene dyes synthesized in this work.
terminal propargylic alcohols 9-ethynyl-9-fluorenol (2g) and
5-ethynyl-5H-dibenzo[a,d]cyclohepten-5-ol (2h), respectively
(Scheme 3).
with 1,1,1,5,5,5-hexafluoro-2,4-pentanedione. The absorption
spectral properties of these compounds, as well as their sol-
vatochromic behaviour, are also discussed.
Characterization of compounds 4a-h was achieved by means of
standard spectroscopic techniques (GC/MS, IR as well as 1H, 13C{1H}
and 19F{1H} NMR) and elemental analyses, all data being fully
consistent with the proposed formulations (details are given in the
Experimental section). Moreover, the structure of 4e could be
unambiguously confirmed by means of a single-crystal X-ray
diffraction analysis. An ORTEP-type drawing of the molecule, along
with selected structural parameters, is shown in Fig. 3. In accord
with the electronic delocalization present in the molecule, the
lengths of the C(5)eC(6) (1.375(4) Å) and C(7)eC(8) (1.380(4) Å)
carbonecarbon double bonds, and the single C(6)eC(7) one (1.417
(4) Å), are respectively longer and shorter than their analogous in
the parent unsubstituted 1,3-butadiene molecule (C]C ¼ 1.341
Å and CeC ¼ 1.463 Å) [12].
2. Results and discussion
2.1. Synthesis and characterization of the novel butadiene dyes
As shown in Scheme 2, using the experimental conditions
optimized in our previous work (i.e. [alkynol]:[diketone]:[TFA]:[Ru]
ratio ¼ 20:200:2:1; 75 ꢁC; sealed tube; solvent-free conditions)
[11], a variety of 1,1-diaryl-4,4-bis(trifluoroacetyl)-1,3-butadienes
(4a-f) could be synthesized in excellent yields (84e98%) starting
from the readily accessible aromatic propargylic alcohols 2a-f and
commercially available 1,1,1,5,5,5-hexafluoro-2,4-pentanedione (3).
A remarkable influence of the electronic properties of the aryl rings
on the reaction rates was observed. Thus, alkynols bearing elec-
tron-donating substituents 2d-f showed less reactivity (9e11 h) as
compared to the unsubstituted one 2a (3 h) [11] or those with
electron-withdrawing functionalities 2b-c (30 min-2 h). As inferred
by monitoring the catalytic reactions by GC, the aldol condensation
The related compound 6a could also be synthesized in high yield
(94%) starting from 1,1-diphenyl-2-propyn-1-ol (2a) and the
commercially available unsymmetric ketone 1,1,1-trifluoro-3-
phenyl-2-propanone 5 (Scheme 4), thus confirming the suitability
of this catalytic transformation for the construction of conjugated
trifluoroacetyl-butadiene frameworks. In accord with our previous
results, the reaction proceeded in a stereoselective manner with
the thermodynamically more stable E isomer being exclusively
formed [11]. In this sense, the stereochemistry of the C]C double
bond in 6a was elucidated by measuring the 3JCH coupling constant
between the initially formed enal and the perfluorinated
diketone is in all cases the rate limiting step of this tandem process,
being favoured with electron-deficient substrates.
Following the same approach, butadiene-diones 4g and 4h were
also selectively synthesized (83e86% yield) by reacting 3 with the
b-
Scheme 1. Ru-catalyzed synthesis of conjugated dienones and diene-diones starting from diaryl-substituted alkynols and enolizable ketones.

J. Borge et al. / Dyes and Pigments 87 (2010) 209e217
211
Scheme 2. Catalytic synthesis of butadiene dyes 4a-f starting from propargylic alcohols 2a-f and 1,1,1,5,5,5-hexafluoro-2,4-pentanedione 3.
(1HeC]Ce13C) associated to the carbonyl carbon of the tri-
fluoroacetyl unit, whose value (6.7 Hz) confirmed a mutually
cis arrangement between the hydrogen atom and the C(]O)CF3
group [13].
spectra were recorded in 23 solvents having different polarities.
Although individual bands in the spectra are usually overlapped
(see, for example, the absorption spectrum of 4f depicted in Fig. 4),
they could be resolved [15] after applying a smoothing spline
algorithm to the observed data followed by a derivative spectros-
copy numerical method (only the negative peaks of the second
derivatives of the smoothed spectra were used for the estimation
of the position of the bands). As shown in Table 2, for both
compounds, the absorption maxima undergo a large red (bath-
ochromic) shift with increasing solvent polarity, i.e. Dlmax z 42 nm
for compound 4e on going from n-hexane to N,N-dimethylforma-
mide and z55 nm for compound 4f on going from n-hexane to
dimethyl sulfoxide. This bathochromic shift of the absorption band,
2.2. Absorption spectra properties
Similarly to other pushepull-type butadienes [6i,j], compounds
4a-h and 6a are coloured materials in the solid state (from yellow to
violet) that display an intense absorption band in the visible region
of their electronic absorption spectra (the absorption maxima and
molar extinction coefficients measured in dichloromethane solu-
tions are collected in Table 1). Replacement of one trifluoroacetyl
unit in 4a (entry 1) by a phenyl group (compound 6a; entry 9)
results in a slight hypsochromic shift (Dlmax ¼ ꢀ17 nm), pointing
out the influence that the number of electron-acceptor tri-
fluoroacetyl residues exerts in the optical properties of these new
dyes.
which corresponds with a
p / p* electronic spectral transition
(see theoretical calculations below) [16] and it is clearly visible to
the naked eye (see Fig. 7), is related to a greater stabilization of the
excited state relative to the ground state with increasing polarity of
the solvent.
Different empirical scales (single and multiparametric) of
solvent polarity have been established in order to quantify, in
a simple way, solvatochromic effects [17]. In this sense, the linear
correlation between the solvatochromism of dyes 4e-f and the
most commonly used solvent polarity scales was investigated
(hypsochromic scales were excluded in this study). The highest
As far as the effect of the para-substituents in compounds 4a-f is
concerned (entries 1e6), a bathochromic shift of the absorption
band is observed when electron-donating groups are present
(Fig. 4), existing a good linear correlation (r ¼ 0.9554) between
Hammett coefficients [14] and lmax values (Fig. 5). Thus, in
complete accord with the valence-bond resonance approach
(Fig. 6), the dipolar excited state in these pushepull dyes is stabi-
lized when X is an electron-donor substituent.
linear correlation was obtained for the
p* scale, introduced by
Kamlet and co-workers [18] and based on the averaged spectral
behaviour of seven nitroaromatic compounds (the adopted math-
ematical model was lmax
¼
l0 þ s
p* [20]; Table 3 and Fig. 8 show
2.3. Solvatochromic behaviour
the results of the least-squares procedure applied to find the best l0
and s values). The linear correlation coefficient r values obtained
(0.9552 (4e) and 0.9659 (4f)) clearly indicate the potential utility of
these butadiene dyes as new solvent polarity indicators [21].
The solvatochromic properties of these new pushepull buta-
diene dyes were evaluated using compounds 4e and 4f, absorbing
in the longest wavelength region, as models. To this end, UVeVis
Scheme 3. Synthesis of butadiene dyes 4g-h.

212
J. Borge et al. / Dyes and Pigments 87 (2010) 209e217
CeC coupling of 1,1-diaryl-2-propyn-1-ols with 1,1,1,5,5,5-hexa-
fluoro-2,4-pentanedione. The positive solvatochromic behaviour of
two representatives (X ¼ OMe, NMe2) was determined by linear
regression analyses of absorption maxima in several solvents of
different polarity, showing a great sensitivity to this effect. Due to
their easy access and their pronounced solvatochromic properties,
these dyes are therefore clear candidates for application as solvent
polarity probes.
4. Experimental
4.1. General
The manipulations were performed under an atmosphere of dry
nitrogen. Solvents were dried by standard methods and distilled
under nitrogen before use. All reagents were obtained from
commercial suppliers and were used without further purification
with the exception of the complex [Ru(h
3-2-C3H4Me)(CO)(dppf)]
[SbF6] (1) [9a] and propargylic alcohols 2b [2c], 2c [23], 2d [24], 2e
[23], 2f [25] and 2h [26], which were prepared using the methods
reported in the literature. Infrared spectra were recorded on a Per-
kineElmer 1720-XFT spectrometer. Elemental C, H and N analyses
were carried out with a PerkineElmer 2400 microanalyzer. UVeVis
spectra were recorded on PerkineElmer Lambda 20 spectrometer.
GC/MS measurements were performed on an Agilent 6890N
equipment coupled to a 5973 mass detector (70 eV electron impact
ionization) using an HP-1 MS column. NMR spectra were recorded
on a Bruker DPX300 instrument at 300 MHz (1H), 282.4 MHz (19F)
or 75.4 MHz (13C) using SiMe4 or CFCl3 as standards. DEPT experi-
ments have been carried out for all the compounds reported in this
paper. All mathematical analysis (smoothing splines, second
derivatives, linear and multilinear regressions) were performed
with MATLAB R2009b.
Fig. 3. ORTEP-type view of the structure of 4e showing the crystallographic labeling
scheme. Thermal ellipsoids are drawn at the 10% probability level. Selected bond
B
distances (Å) and angles ( ): C(1)-C(2) ¼ 1.540(5); C(2)eO(2) ¼ 1.206(4); C(2)eC
(5) ¼ 1.454(4); C(3)eC(4) ¼ 1.559(5); C(4)eO(1) ¼ 1.206(4); C(4)eC(5) ¼ 1.465(4);
C(5)eC(6) ¼ 1.375(4); C(6)eC(7) ¼ 1.417(4); C(7)eC(8) ¼ 1.380(4); C(8)eC(9) ¼ 1.480
(4); C(8)eC(16) ¼ 1.469(4); C(1)eC(2)eO(2) ¼ 115.5(3); C(1)eC(2)eC(5) ¼ 120.4(3);
C(3)eC(4)eO(1) ¼ 115.3(3); C(3)eC(4)eC(5) ¼ 120.2(3); C(2)eC(5)eC(4) ¼ 117.0(3);
C(2)eC(5)eC(6) ¼ 122.2(3); C(4)eC(5)eC(6) ¼ 120.8(3); C(5)eC(6)eC(7) ¼ 129.2(3); C
(6)eC(7)eC(8) ¼ 122.6(3); C(7)eC(8)eC(9) ¼ 121.9(3); C(7)eC(8)eC(16) ¼ 119.9(3);
C(9)eC(8)eC(16) ¼ 118.3(2).
2.4. Quantum chemical calculations
The electronic structure of these new dyes was further examined
by theoretical models implanted in the Gaussian 03 program [22].
In particular, density functional theory (DFT) calculations (B3LYP/6-
31G) were carried out to obtain information about the energy
and electron distribution in the frontier MOs of 4e (see Fig. 9). As
expected, calculations clearly revealed that HOMOeLUMO excita-
tion moves the electron distribution from the aromatic part of the
molecule to the acceptor bis(trifluoroacetyl) moiety, the calculated
energy gap (3.11 eV) being in good agreement with the UV/Vis data
experimentally obtained for this compound. The redistribution of
the electron density during the HOMOeLUMO electron transition
determines the influence on the colour properties of these buta-
diene dyes of factors such as the effect of the substituents on
the aromatic rings, or the interaction with solvents (solvatochromic
behaviour).
4.2. Synthesis of compounds 4a-h
The catalyst [Ru(h
3-2-C3H4Me)(CO)(dppf)][SbF6] (1) (0.049 g,
0.05 mmol), the corresponding propargylic alcohol 2a-h (1 mmol),
1,1,1,5,5,5-hexafluoro-2,4-pentanedione (3; 1.41 mL, 10 mmol) and
trifluoroacetic acid (TFA) (7.4 mL, 0.1 mmol) were introduced into
a sealed tube under a nitrogen atmosphere. The reaction mixture
was heated at 75 ꢁC for the indicated time (the reaction was
monitored by regular sampling and analysis by GC/MS). After
removal of volatiles under vacuum, the residue was purified by
column chromatography (silica gel) using a mixture EtOAc/hexane
(1:10) as eluent. Characterization data for compound 4a were
already included in our previous article [11].
4.2.1. 3-(3,3-Bis(4-fluorophenyl)allylidene)-1,1,1,5,5,5-
hexafluoro-2,4-pentanedione (4b)
3. Conclusions
Yellow oil; Reaction time: 30 min; Yield: 0.365 g (84%); Anal.
Calcd for C20H10F8O2 (434.28 g molꢀ1): C, 55.31; H, 2.32%. Found:
In summary, a new series of pushepull butadiene dyes, i.e. (4-
C6H4X)2C]CHeCH]C(COCF3)2, has been synthesized by catalytic
C, 55.45; H, 2.28%; IR (Nujol):
(s, C]O); 1H NMR (CDCl3):
n
/cmꢀ1 ¼ 1570 (m, C]C), 1678
3
d
¼ 7.04 and 7.72 (d, JHH ¼ 12.2 Hz,
Scheme 4. Catalytic synthesis of 6a starting from alkynol 2a and 1,1,1-trifluoro-3-phenyl-2-propanone (5).

J. Borge et al. / Dyes and Pigments 87 (2010) 209e217
213
Table 1
Light absorption properties of butadiene dyes 4a-h and 6a.a
Entry
Compound
lmax (nm)
3 )
(Mꢀ1 cmꢀ1
1
2
3
4
5
6
7
8
9
4a
4b
4c
4d
4e
4f
4g
4h
6a
388
389
390
405
447
577
412
420
371
25 621
13 502
16 238
22 010
30 047
21 132
28 953
10 543
29 661
a
Measured in dichloromethane.
Fig. 5. lmax vs Hammett coefficients for compounds 4a-f.
1H each, ]CH), 7.10e7.40 (m, 8H, Harom); 13C{1H} NMR (CDCl3):
4.2.3. 3-(3,3-Bis(4-methylphenyl)allylidene)-1,1,1,5,5,5-
hexafluoro-2,4-pentanedione (4d)
d
¼ 115.3 (q, 1JCF ¼ 291.6 Hz, CF3), 116.1 (q, 1JCF ¼ 290.6 Hz, CF3),
3
3
116.2 (d, JCF ¼ 9.7 Hz, CHarom), 116.4 (d, JCF ¼ 9.5 Hz, CHarom),
Orange oil; Reaction time: 11 h; Yield: 0.401 g (94%); Anal.
2
Calcd for C22H16F6O2 (426.35 g molꢀ1): C, 61.98; H, 3.78%. Found:
120.9 (s, ]CH), 127.2 (s, ]C), 131.8 (d, JCF ¼ 8.8 Hz, CHarom),
2
C, 62.12; H, 3.85%; IR (Nujol):
n
/cmꢀ1 ¼ 1550 (m, C]C), 1696
133.0 (d, JCF ¼ 8.0 Hz, CHarom), 136.1 and 136.2 (s, Carom), 150.7
1
(s, C]O); 1H NMR (CDCl3):
d
¼ 2.44 and 2.51 (s, 3H each, CH3),
(br, ]CH), 162.2 (s, ]C), 163.4 (d, JCF ¼ 63.7 Hz, CFarom), 165.9
1
2
3
(d, JCF ¼ 65.8 Hz, CFarom), 178.7 (q, JCF ¼ 36.6 Hz, CO), 184.5
6.93 (d, JHH ¼ 11.7 Hz, 1H, ]CH), 7.11e7.35 (m, 8H, CHarom), 7.87
(q, JCF ¼ 38.7 Hz, CO); 19F{1H} NMR (CDCl3):
d
¼ ꢀ111.2 and
2
(dq, JHH ¼ 11.7 Hz, JHF ¼ 1.0 Hz, 1H, ]CH); 13C{1H} NMR
3
5
1
ꢀ109.7 (m, 1F each, CFarom), ꢀ78.1 and ꢀ74.1 (s, 3F each, CF3); MS
(EI 70eV): m/z (%) ¼ 434 (15) [Mþ], 365 (10), 337 (20), 268 (10),
240 (30), 227 (100), 201 (15).
(CDCl3):
d
¼ 21.7 and 21.8 (s, CH3), 115.5 (q, JCF ¼ 291.6 Hz, CF3),
1
116.3 (q, JCF ¼ 290.5 Hz, CF3), 120.2 (s, ]CH), 125.9 (s, ]C),
129.6, 129.9, 130.1 and 131.3 (s, CHarom), 134.5, 137.6, 141.3 and
142.6 (s, Carom), 152.3 (br, ]CH), 165.9 (s, ]C), 178.9
(q, JCF ¼ 35.6 Hz, CO), 184.7 (q, JCF ¼ 38.7 Hz, CO); 19F{1H} NMR
2
2
4.2.2. 3-(3,3-Bis(4-chlorophenyl)allylidene)-1,1,1,5,5,5-hexafluoro-
2,4-pentanedione (4c)
(CDCl3):
d
¼ ꢀ76.1 and ꢀ72.1 (s, 3F each, CF3); MS (EI 70eV): m/z
(%) ¼ 426 (20) [Mþ], 411 (10), 357 (10), 329 (40), 311 (10), 260
Yellow oil; Reaction time: 2 h; Yield: 0.430 g (92%); Anal. Calcd
for C20H10F6Cl2O2 (467.19 g molꢀ1): C, 51.42; H, 2.16%. Found: C,
(10), 233 (40), 219 (100), 202 (15).
51.56; H, 2.19%; IR (Nujol):
n
/cmꢀ1 ¼1575 (m, C]C), 1699 (s, C]O);
1H NMR (CDCl3):
d
¼ 7.03 (d, 3JHH ¼ 12.2 Hz,1H, ]CH), 7.20 and 7.52
4.2.4. 3-(3,3-Bis(4-methoxyphenyl)allylidene)-1,1,1,5,5,5-
hexafluoro-2,4-pentanedione (4e)
(d, 3JHH ¼ 8.6 Hz, 2H each, CHarom), 7.29 and 7.40 (d, 3JHH ¼ 8.8 Hz,
2H each, CHarom), 7.71 (dq, 3JHH ¼ 12.2 Hz, 5JHF ¼ 1.0 Hz, 1H, ]CH);
Orange solid; Reaction time: 9 h; Yield: 0.449 g (98%); Anal.
Calcd for C22H16F6O4 (458.35 g molꢀ1): C, 57.65; H, 3.52%. Found:
13C{1H} NMR (CDCl3):
d
¼ 115.3 and 116.1 (q, 1JCF ¼ 291.1 Hz, CF3),
C, 57.72; H, 3.60%; IR (Nujol):
n
/cmꢀ1 ¼1539 (m, C]C),1685 (s, C]O);
121.3 (s, ]CH),129.5, 129.6,130.8 and 132.3 (s, CHarom),129.0 (s, ]C),
131.6,137.3, 138.1 and 138.3 (s, Carom),150.1 (br, ]CH), 161.5 (s, ]C),
178.7 (q, 2JCF ¼ 36.5 Hz, CO), 184.39 (q, 2JCF ¼ 39.0 Hz, CO); 19F{1H}
1H NMR (CDCl3):
d
¼ 3.87 and 3.91 (s, 3H each, OCH3), 6.92 and 7.01
3
3
(d, JHH ¼ 8.8 Hz, 2H each, CHarom), 7.05 (d, JHH ¼ 12.2 Hz, 1H, ]
3
CH), 7.20 and 7.35 (d, JHH ¼ 8.8 Hz, 2H each, CHarom), 7.79 (dq,
NMR (CDCl3):
d
¼ ꢀ76.2 and ꢀ72.2 (s, 3F each, CF3); MS (EI 70eV):
5
3JHH ¼ 12.2 Hz, JHF ¼ 1.0 Hz, 1H, ]CH); 13C{1H} NMR (CDCl3):
m/z (%) ¼ 466 (10) [Mþ], 431 (10), 397 (10), 369 (15), 334 (10), 299
d
¼ 55.7 and 55.8 (s, OCH3), 114.3, 114.6, 132.1 and 133.2 (s, CHarom),
(10), 276 (20), 259 (100), 236 (40), 202 (80).
115.5 (q, 1JCF ¼ 291.9 Hz, CF3), 116.4 (q, 1JCF ¼ 291.1 Hz, CF3), 119.2 (s,
]CH), 124.6 (s, ]C), 129.7, 132.9, 162.1 and 162.9 (s, Carom), 152.9
2
(br, ]CH), 165.8 (s, ]C), 178.7 (q, JCF ¼ 35.7 Hz, CO), 184.9
2
(q, JCF ¼ 38.1 Hz, CO); 19F{1H} NMR (CDCl3):
d
¼ ꢀ76.0 and ꢀ71.9
(s, 3F each, CF3); MS (EI 70eV): m/z (%) ¼ 458 (30) [Mþ], 389 (20),
361 (60), 264 (40), 251 (100), 226 (10), 206 (10).
4.2.5. 3-(3,3-Bis(4-(dimethylamino)phenyl)allylidene)-1,
1,1,5,5,5-hexafluoro-2,4-pentanedione (4f)
Violet solid; Reaction time: 11 h; Yield: 0.451 g (93%); Anal.
Calcd for C24H22F6N2O2 (484.43 g molꢀ1): C, 59.50; H, 4.52; N,
5.78%. Found: C, 59.63; H, 4.48; N, 5.85%; IR (Nujol):
n
/cmꢀ1 ¼1517
(m, C]C), 1597 (s, C]O); 1H NMR (CDCl3):
d
¼ 3.10 and 3.11 (s, 6H
each, CH3), 6.67e6.76 (m, 3H, CHarom), 7.03 (d, 3JHH ¼ 12.2 Hz, 1H, ]
CH), 7.20e7.34 (m, 3H, CHarom), 7.76e7.85 (m, 2H, CHarom), 8.17 (dq,
3JHH ¼ 12.2 Hz, JHF ¼ 1.0 Hz, 1H, ]CH); 13C{1H} NMR (CDCl3):
5
d
¼ 40.2 and 40.3 (s, CH3), 111.3, 111.6, 133.4 and 134.3 (s, Carom),
115.0 and 116.0 (q, 1JCF ¼ 291.5 Hz, CF3),117.2 (s, ]CH), 119.1 (s, ]C),
130.9, 132.9, 152.6 and 153.2 (s, Carom), 155.1 (br, ]CH), 170.4 (s, ]C),
173.0 (q, JCF ¼ 34.5 Hz, CO), 176.5 (q, JCF ¼ 35.5 Hz, CO); 19F{1H}
2
2
NMR (CDCl3):
d
¼ ꢀ75.2 and ꢀ74.9 (s, 3F each, CF3); MS (EI 70 eV):
m/z (%) ¼ 484 (100) [Mþ], 465 (5), 440 (20), 415 (5), 387 (10), 364
Fig. 4. UVeVis spectra of compounds 4a-f recorded in dichloromethane solution.
(50), 294 (15), 238 (20), 202 (10).

214
J. Borge et al. / Dyes and Pigments 87 (2010) 209e217
Fig. 6. The electronic conjugation in dyes 4a-f.
Table 2
4.2.6. 3-(2-Fluoren-9-ylidene-ethylidene)-1,1,1,5,5,5-hexafluoro-
2,4-pentanedione (4g)
lmax (nm) values of dyes 4e and 4f in various solvents and p
* values of solvents.a
Orange solid; Reaction time: 5 h; Yield: 0.329 g (83%); Anal.
Solvent
Compound 4e
Compound 4f
p*
Calcd for C20H10F6O2 (396.28 g molꢀ1): C, 60.62; H, 2.54%. Found: C,
n-Hexane
420
431
436
442
440
441
440
445
eeeb
446
448
eeeb
449
447
448
453
443
447
462
461
462
459
eeeb
531
543
553
566
570
570
562
563
570
565
570
569
573
573
573
574
571
577
586
583
581
583
586
ꢀ0.11
0.21
0.24
0.45
0.47
0.48
0.49
0.49
0.54
0.55
0.55
0.60
0.60
0.62
0.66
0.68
0.69
0.73
0.86
0.87
0.88
0.88
1.00
60.74; H, 2.61%; IR (Nujol):
1H NMR (CDCl3):
n
/cmꢀ1 ¼1544 (m, C]C), 1690 (s, C]O);
Carbon tetrachloride
Diethyl ether
Ethyl acetate
1-Butanol
2-Propanol
1,4-Dioxane
Toluene
Ethanol
Benzene
Tetrahydrofuran
Methanol
2-Butanone
Acetone
Acetonitrile
Chlorobenzene
Chloroform
Dichloromethane
Nitrobenzene
Pyridine
N,NeDimethylformamide
Benzonitrile
Dimethyl sulfoxide
3
d
¼ 7.21 (d, JHH ¼ 12.7 Hz, 1H, ]CH); 7.27e7.36
(m, 2H, CHarom), 7.41e7.48 (m, 2H, CHarom), 7.58e7.66 (m, 3H,
CHarom), 7.78 (d, 3JHH ¼ 7.8 Hz, 1H, CHarom), 8.81 (dq, 3JHH ¼ 12.7 Hz,
5JHF ¼ 1.0 Hz, 1H, ]CH); 13C{1H} NMR (CDCl3):
d
¼ 115.2 and 116.3
1
(q, JCF ¼ 291.1 Hz, CF3), 117.0 (s, ]CH), 120.7, 121.2, 123.1, 126.9,
128.5, 128.6, 132.3 and 132.5 (s, CHarom), 129.0 (s, ]C), 135.7, 138.2,
141.6 and 143.5 (s, Carom), 146.8 (br, ]CH), 153.8 (s, ]C), 178.6 (q,
2JCF ¼ 36.5 Hz, CO), 184.2 (q, JCF ¼ 39.0 Hz, CO); 19F{1H} NMR
2
(CDCl3):
d
¼ ꢀ76.3 and ꢀ71.7 (s, 3F each, CF3); MS (EI 70eV): m/z
(%) ¼ 396 (70) [Mþ], 376 (10), 327 (30), 299 (10), 257 (60), 229 (10),
202 (100), 186 (10).
4.2.7. 3-(2-Dibenzo[a,d]cyclohepten-5-ylidene-ethylidene)-
1,1,1,5,5,5-hexafluoro-2,4-pentanedione (4h)
Orange solid; Reaction time: 1.5 h; Yield: 0.405 g (96%); Anal.
Calcd for C22H12F6O2 (422.32 g molꢀ1): C, 62.57; H, 2.86%. Found: C,
62.41; H, 2.95%; IR (Nujol):
n
/cmꢀ1 ¼1579 (m, C]C), 1699 (s, C]O);
1H NMR (CDCl3):
d
¼ 6.64 (d, 3JHH ¼ 12.0 Hz, 1H, ]CH); 6.99 (br, 2H,
a
Spectra recorded using 6 ꢂ 10ꢀ5 M solutions.
p* values taken from reference
3
CH]CH), 7.31 (d, JHH ¼ 7.1 Hz, 1H, CHarom), 7.40e7.56 (m, 7H,
[17] with the exception of those of benzonitrile and 2-butanone which were
obtained from reference [19].
3
CHarom), 7.72 (d, JHH ¼ 12.0 Hz, 1H, ]CH); 13C{1H} NMR (CDCl3):
b
A broad absorption band was observed avoiding accurate lmax determination.
d
¼ 115.3 and 116.1 (q, 1JCF ¼ 291.1 Hz, CF3), 126.3 (s, ]CH), 127.2,
128.5, 129.3, 129.4, 129.5, 129.8, 130.1, 130.4, 131.2 and 131.6
(s, CHarom and CH]CH), 127.5 (s, ]C), 133.8, 134.0, 135.0 and 139.5
2
(s, Carom), 150.5 (br, ]CH), 163.8 (s, ]C), 178.8 (q, JCF ¼ 36.5 Hz,
2
CO), 184.4 (q, JCF ¼ 39.0 Hz, CO); 19F{1H} NMR (CDCl3):
d
¼ ꢀ76.3
and ꢀ72.2 (s, 3F each, CF3); MS (EI 70eV): m/z (%) ¼ 422 (15) [Mþ],
353 (10), 325 (50), 256 (10), 229 (50), 215 (100), 203 (10), 189 (15).
Fig. 7. Photograph showing the colour change of dye 4f when dissolved in solvents
with different polarity.
Table 3
Fitting results.a
Compound
l0
s
r
4e
4f
423.23 (3.80)
539.62 (3.90)
40.34 (6.19)
50.69 (6.17)
0.9552
0.9659
a
Values in parentheses represent the 95% confidence limits.
Fig. 8. lmax vs p* values for dyes 4e and 4f (fitting results superimposed).

J. Borge et al. / Dyes and Pigments 87 (2010) 209e217
215
Fig. 9. Surface and energy of the frontier molecular orbitals of dye 4e.
4.3. Synthesis of (Z)-1,1,1-trifluoro-3,6,6-triphenylhexa-3,5-
dien-2-one (6a)
(Nujol):
n
/cmꢀ1 ¼ 1576 (m, C]C), 1679 (s, C]O); 1H NMR (CDCl3):
3
d
¼ 6.78 (d, JHH ¼ 11.5 Hz, 1H, ]CH), 7.21e7.51 (m, 15H, CHarom),
7.66 (dq, JHH ¼ 11.5 Hz, JHF ¼ 1.2 Hz, 1H, ]CH); 13C{1H} NMR
3
5
1
The catalyst [Ru(
h
3-2-C3H4Me)(CO)(dppf)][SbF6] (1) (0.049 g,
(CDCl3):
d
¼ 116.1 (q, JCF ¼ 291.9 Hz, CF3), 122.8 (s, ]CH), 127.5,
0.05 mmol), the propargylic alcohol 2a (0.208 g, 1 mmol), 1,1,1-
trifluoro-3-phenyl-2-propanone (5; 1.54 mL, 10 mmol) and tri-
127.6, 127.7, 127.9, 128.3, 128.7, 129.6 and 129.8 (s, CHarom), 132.6
(s, ]C), 134.0, 137.4 and 140.1 (s, Carom), 143.6 (br, ]CH), 155.0
2
fluoroacetic acid (TFA) (7.4
mL, 0.1 mmol) were introduced into
(s, ]C), 179.7 (q, JCF ¼ 33.2 Hz, CO); 19F{1H} NMR (CDCl3):
a sealed tube under a nitrogen atmosphere. The reaction mixture
was heated at 75 ꢁC for 11 h (the reaction was monitored by regular
sampling and analysis by GC/MS). After removal of volatiles under
vacuum, the residue was purified by column chromatography
(silica gel) using a mixture EtOAc/hexane (1:10) as eluent, affording
6a as a yellow solid. Yield: 0.356 g (94%); Anal. Calcd for C24H17F3O
(378.39 g molꢀ1): C, 76.18; H, 4.53%. Found: C, 76.30; H, 4.61%; IR
d
¼ ꢀ70.3 (s, 3F, CF3); MS (EI 70eV): m/z (%) ¼ 378 (60) [Mþ], 309
(60), 281 (40), 265 (50), 231 (15), 203 (100), 187 (15), 165 (20).
4.4. X-ray crystal structure determination of compound 4e
Crystals suitable for X-ray diffraction analysis were obtained by
slow evaporation of a saturated solution of 4e in dichloromethane.
Data collection, crystal and refinement parameters are collected in
Table 4. Diffraction data were recorded at 150(2) K on a Nonius
KappaCCD single-crystal diffractometer, using Mo-Ka radiation
Table 4
Crystal data and structure refinement for 4e.
(
l
¼ 0.71073 Å). Images were collected at a 35 mm fixed crystal-
detector distance, using the oscillation method, with 1ꢁ oscillation
and 100 s exposure time per image. Data collection strategy was
calculated with the program Collect [27]. Data reduction and cell
refinement were performed with the programs HKL Denzo and
Scalepack [28]. A semi-empirical absorption correction was applied
using the program SORTAV [29].
Empirical formula
Formula weight
Temperature (K)
Wavelength (Å)
Crystal system
Space group
Unit cell dimensions
a (Å)
C22H16F6O4
458.35
293(2)
0.71073
Monoclinic
P21
10.1478(6)
The software package WINGX [30] was used for space group
determination, structure solution and refinement. Crystal structure
was solved by direct methods, using the program SIR-92 [31].
Anisotropic least-squares refinement was carried out with SHELXL-
97 [32]. All non-hydrogen atoms were anisotropically refined. The
hydrogen atoms were geometrically placed riding on their parent
atoms with isotropic displacement parameters set to 1.2 times the
Ueq of the atoms to which they are attached (1.5 for methyl groups).
b (Å)
5.5480(2)
c (Å)
18.3854(11)
90
93.154(3)
90
a
b
g
(ꢁ)
(ꢁ)
(ꢁ)
Volume (Å3)
1033.53(9)
Z
2
Density (calculated) (g cmꢀ3
)
1.473
0.136
468
Absorption coefficient (mmꢀ1
F(000)
)
P
P
The function minimized was ½ wðFo2 ꢀ Fc2Þ= wðFo2Þꢃ1=2 where
w ¼ 1=½s2ðFo2Þ þ ð0:0889PÞ2ꢃ with
s
2(Fo2) from counting statistics
Crystal size (mm)
0.35 ꢂ 0.15 ꢂ 0.105
Theta range for data collection (ꢁ)
Index ranges
2.01e25.59
and P ¼ ðmaxðFo2; 0Þ þ 2Fc2Þ=3. Atomic scattering factors were
taken from the International Tables for X-Ray Crystallography [33].
The crystallographic plots were made with PLATON [34].
ꢀ12 ꢄ h ꢄ 12
ꢀ6 ꢄ k ꢄ 6
0 ꢄ l ꢄ 22
Reflections collected/unique
Completeness to theta ¼ 25.59ꢁ
Refinement method
10 658/3843 [R(int) ¼ 0.0389]
99.3%
Full-matrix least-squares on F2
5. Supplementary material
Data/restraints/parameters
3843/1/291
1.040
0.0427
0.1143
0.0661
Goodness-of-fit on F2
Crystallographic data for the structural analysis of compound 4e
have been deposited with the Cambridge Crystallographic Data
Centre, CCDC no. 758966. Copies of this information may be
obtained free of charge from The Director, CCDC, 12 Union Road,
Cambridge CB2 1EZ, UK (Fax: þ44-1223-336033; e-mail: deposit@
ccdc.cam.ac.uk or www: http://www.ccdc.cam.ac.uk).
R1a [I > 2
s
(I)]
wR2a [I > 2
(I)]
R1 (all data)
s
wR2 (all data)
0.1451
0.228 and ꢀ0.260
Largest difference peak and hole (eÅꢀ3
)
P
P
P
P
R1 ¼
jðjFoj ꢀ jFcjÞj= jFoj; wR2 ¼ f ½wðFo2 ꢀ Fc2Þ2ꢃ= ½wðFo2Þ2ꢃg1=2
.
a

216
J. Borge et al. / Dyes and Pigments 87 (2010) 209e217
rings using fluorine-containing 3,4-dihydro-2H-pyrans.
A
facile synthetic
Acknowledgments
method for 1,1,1,5,5,5-hexafluoro-3-[(E)-3-arylallylidene]-pentane-2,4-dio-
nes. Heterocycles 2008;76:215e9.
Financial support from the Spanish MICINN (Projects CTQ2006-
08485/BQU, CTQ2009-08746/BQU, FIS2006-04049 and Consolider
Ingenio 2010 (CSD2007-00006)) and the Gobierno del Principado
de Asturias (FICYT Project IB08-036) is acknowledged. S.E.G.-G.
thanks MICINN and the European Social Fund for the award of
a Ramón y Cajal contract. The assistance of Drs. José Manuel Recio
and Ruth Álvarez-Uría with the theoretical calculations is also
gratefully acknowledged.
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