Synthesis and structures of crystalline solvates formed of pyridinium N-phenoxide (Reichardt's-type) betaine dyes and alcohols

Article abstract of DOI:10.1039/b9nj00540d

Four new betaine dyes of the Reichardt's type featuring two tolyl substituents in different attachment (2-4) or being an analogous 1-naphthyl derivative (5) have been synthesized and described with reference to their negative solvatochromism. The dinaphth

Full text of DOI:10.1039/b9nj00540d

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www.rsc.org/njc | New Journal of Chemistry
Synthesis and structures of crystalline solvates formed of pyridinium
N-phenoxide (Reichardt’s-type) betaine dyes and alcoholsw
Sandra Kurjatschij, Wilhelm Seichter and Edwin Weber*
Received (in Montpellier, France) 7th October 2009, Accepted 1st February 2010
First published as an Advance Article on the web 14th April 2010
DOI: 10.1039/b9nj00540d
Four new betaine dyes of the Reichardt’s type featuring two tolyl substituents in different
attachment (2–4) or being an analogous 1-naphthyl derivative (5) have been synthesized and
described with reference to their negative solvatochromism. The dinaphthyl derivative 5 and also
a corresponding intermediate nitrophenol 9d were shown with variable-temperature NMR
spectroscopy to form conformational atropisomers in solution. Crystal structures of seven
alcoholic solvent complexes including the unsubstituted parent compound (1) and different
alcohols [1ÁEtOH (1 : 1), 1Ái-PrOH (1 : 1), 2ÁMeOH (1 : 2), 3Ái-PrOH (1 : 1), 3Án-BuOH (1 : 1),
4ÁEtOH (1 : 2) and 5ÁMeOH (1 : 3)] have been studied using X-ray diffraction methods. The
betaine dyes exist as genuine zwitterion ground state structures in the solid state with twisted
conformation between the phenoxide and pyridinium rings. With the exception of 3a
[3Ái-PrOH (1 : 1)], the alcohol guests in the complexes are hydrogen bonded to the oxygen atom of
the phenoxide units, whereas in the i-PrOH complex of 3, the alcohol forms trimeric clusters
without specific interaction with the betaine framework. From the packing modes in the crystals,
the solvated betaines may be classified either as co-ordination type inclusion compounds with
pocket-like host arrangements [1ÁEtOH (1 : 1), 1Ái-PrOH (1 : 1), 2ÁMeOH (1 : 2), 3Án-BuOH (1 : 1),
4ÁEtOH (1 : 2) and 5ÁMeOH (1 : 3)], or a true clathrate with channel-type topology
[3Ái-PrOH (1 : 1)].
determination of a bromo-substituted derivative of the parent
betaine dye 1 as an ethanol solvate,15 a recent structure of the
Introduction
hydrate of a substituted derivative of 116 and of a related
Pyridinium N-phenoxide betaine dyes, commonly known as
the Reichardt’s type dyes,1 are of great interest due to the
ortho-betaine.12 A number of pyridinium salts of the Reichardt’s
phenomena of solvatochromism, thermochromism, piezo-
compounds formed with different acids, in some cases containing
chromism, and halochromism.2 That is, the position of their
solvent molecules in the crystal lattice, have also been
longest wavelength intermolecular charge-transfer absorption
band of their UV-vis absorption spectra depends on solvent
polarity, solution temperature, external pressure, and on the
nature and concentration of added salts.3 The standard
pyridinium N-phenoxide betaine dye 1 (Scheme 1) exhibiting
extraordinarily large negative solvatochromism has been used
to set up an empirical scale of solvent polarity [ET(30)
values]4,5 to probe micellar environments6 and to determine
the composition of binary solvent mixtures7 including the
amount of water in organic solvents.8 Moreover, chemical
sensor development9 and other materials’ design10,11 have
taken advantage of the particular behavior of the betaine dyes.
This has stimulated the synthesis of a large number of
different pyridinium N-phenoxide betaine dyes with special
and improved properties.3,5,12,14 Nevertheless, solid state
structures of the Reichardt’s type dyes have only scarcely been
investigated, except for the early X-ray crystal structure
Institut fur Organische Chemie, Technische Universitat Bergakademie
¨
¨
Freiberg, Leipziger Str. 29, D-09596 Freiberg/Sachsen, Germany.
E-mail: edwin.weber@chemie.tu-freiberg.de;
Fax: +49 (0) 37 31-39 31 70
w CCDC reference numbers 746916–746922. For crystallographic data
in CIF or other electronic format see DOI: 10.1039/b9nj00540d
Scheme 1 Betaine dyes and solvent complexes studied.
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reported,17–20 but they do not really feature the typical betaine
structure under discussion here. Similar relations have recently
been shown for the crystalline complexes of several other
betaines.21–24 Remarkably, the known crystal structures of
the Reichardt’s type betaines demonstrate twisted conformations
of the p-systems, thus giving rise to impairment of the
conjugation and asking for more details of structural studies.
Moreover, discovering the modes of supramolecular contacts25–27
between the betaine dye and interacting solvent molecules is
another interesting target.
In the current work, we describe the synthesis of the new
betaine dyes 2–5 (Scheme 1) and report on the X-ray structures
of seven crystalline solvent complexes that involve the betaine
dyes 1–5 with different alcohols included in the crystal lattice,
i.e. 1a [1ÁEtOH (1 : 1)], 1b [1Ái-PrOH (1 : 1)], 2a [2ÁMeOH (1 : 2),
3a [3Ái-PrOH (1 : 1)], 3b [3Án-BuOH (1 : 1)], 4a [4ÁEtOH (1 : 2)],
and 5a [5ÁMeOH (1 : 3)]. We report also on the stereoisomerism
of the dinaphthyl-substituted betaine 5 and the corresponding
p-nitrophenol intermediate 9d based on variable temperature
NMR studies, giving information on the rotational barriers in
these molecules.
Results and discussion
Synthesis
The synthesis of the new Reichardt’s type betaine dyes 2–5
(Scheme 2) was accomplished following on principle the
established procedures for the preparation of para-pyridinium
N-phenoxides.4,28,29 Here, the respective 2,6-diaryl-substituted
4-aminophenols 10a–d, obtained by hydrogenation of the
corresponding nitrophenols 9a–d, were condensed with 2,4,6-
triphenylpyrylium hydrogen sulfate (11) in the presence of
sodium acetate to give, on addition of sodium hydroxide, the
respective betaines. The nitrophenols 9a–d were obtained by
condensation reaction between 2-nitromalonaldehyde-Na (8)
and the corresponding 1,3-diaryl-substituted propan-2-ones
7a–d.30 The ketones 7a–d were synthesized from 6a–d using
two alternative literature procedures specified as A31 and B32
in Scheme 2. Process A involves a historical solid state
distillation of the calcium salts of the correspondingly aryl-
substituted acetic acids, while the more recently developed
process B represents a reaction of the respective arylacetic
acid with N,N-dicyclohexylcarbodiimide (DCC) catalyzed
by 4-N,N-dimethylaminopyridine (4-DMAP). The yields
obtained are moderate but were found higher in the case of
B (Scheme 2).
Scheme 2 Reaction scheme for the synthesis of the betaine dyes 2–5.
[4ÁEtOH (1 : 2)] and 5a [5ÁMeOH (1 : 3)] are given in Table 1.
Structural features of the betaine dye molecules, including
torsion angles and selected bond lengths, are shown in Table 2.
Geometric parameters of possible intermolecular hydrogen
bond interactions are presented in Table 3. The solvent
molecules in 3a and 3b, as well as one of the ethanol molecules
in 4a, are disordered and turned out to be difficult to refine. In
order to gain reasonable molecular geometries, bond lengths
were restrained to ideal values.
The conformation of the betaine dye molecules 1–5 in their
solvate structures can be described by a set of six torsion
angles, denoted as t1–t6 in Scheme 3 (Table 2). In this
connection, particular interest focuses on the conformational
features that involve the molecular fragment given by the rings
I and II, which are of opposite electronic nature. The bond
distances in the molecules are in good agreement with those
found in the crystal structures of related compounds.15,16
A
Reichardt’s type betaines were shown to crystallize as
hydrates14,16,28,29 or containing another solvent of crystallization.15
This is also a characteristic feature of the betaines 2–5 being
isolated as hydrates or stoichiometric complexes with alcohols
(MeOH, EtOH, i-PrOH, n-BuOH) on crystallization from
these solvents. Representative complexes (Scheme 1) have
been studied in view of their X-ray crystal structures that are
discussed below.
detailed analysis reveals that the C–O bonds of the betaines
are significantly shortened in comparison with those of the
protonated derivatives (phenolic pyridinium salts)18–20
[1.268(3)–1.307(4) vs.1.336–1.364 A], whereas the C–N bond
length between the aromatic rings I and II (Scheme 3) seems to
be less affected by deprotonation of the phenolic group. The
contraction of the C–O bond and the elongation of the
neighbouring C–C bonds indicate a partial quinoid character
of the phenolate ring. The pyridinium and the phenolate rings
are not co-planar, but twisted. The dihedral angle formed
by their ring planes ranges between 55.2(1) and 74.6(2)1.
X-ray structural studies
Crystal data for 1a [1ÁEtOH (1 : 1)], 1b [1Ái-PrOH (1 : 1)], 2a
[2ÁMeOH (1 : 2), 3a [3Ái-PrOH (1 : 1)], 3b [3Án-BuOH (1 : 1)], 4a
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Table 1 Crystallographic and structure refinement data of the compounds studied
Compound
1a
1b
2a
3a
3b
4a
5a
Empirical formula
C41H29NOÁ
C2H6O
597.72
Bluish-violet
Monoclinic
P21/n
10.1428(3)
19.0295(6)
17.0312(5)
90.0
102.607(2)
90.0
3207.98(17)
4
1264
1.238
0.075
C
41H29NOÁ
C
43H33NOÁ
C
43H33NOÁ
C
C4H10
653.82
Blue
Monoclinic
P21/c
8.8952(2)
18.8888(3)
21.0329(4)
90.0
90.084(1)
90.0
3533.94(12)
4
1392
43H33NOÁ
C
43H33NOÁ
C
49H33NOÁ
C3H8O
611.75
Blue
Monoclinic
P21/n
10.4500(7)
19.7456(11)
16.6334(9)
90.0
105.934(3)
90.0
3300.3(3)
4
1296
1.231
0.074
2 CH4O
643.79
Redish-violet Blue
Monoclinic
P21/c
10.8713(2)
16.8352(4)
18.9751(4)
90.0
92.713(1)
90.0
3468.94(13)
4
1368
1.233
0.076
C3H8O
639.80
O
2 C2H6O
671.84
Bluish-violet
Monoclinic
P21/n
11.9196(3)
19.0346(4)
16.6949(5)
90.0
98.110(1)
90.0
3749.94(17)
4
1432
1.190
0.073
3 CH4O
747.89
Redish-violet
Monoclinic
P21/c
13.2600(5)
17.3132(6)
18.2974(6)
90.0
104.518(2)
90.0
4066.5(3)
4
1584
1.222
0.076
Formula weight
Colour
Crystal system
Space group
a/A
b/A
c/A
Rhombohedral
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R3c
18.822(1)
18.822(1)
18.822(1)
104.15(1)
104.15(1)
104.15(1)
5932.3(5)
6
a (1)
b (1)
g (1)
V/A3
Z
V(000)
2040
1.075
0.500
Vc/mg mÀ3
)
1.229
0.074
m/mmÀ1
Data collection
T/K
No. of collected reflections 41306
90(2)
90(2)
22167
1.6–26.4
93(2)
32121
1.6–26.4
193(2)
10111
3.0–65.0
123(2)
87340
1.4–29.1
123(2)
39398
1.6–29.1
90(2)
34681
1.6–26.4
Within the y-limit (1)
1.6–29.1
Index ranges Æh, Æk, Æl
À13/13, À26/18, À12/6, À24/24, À13/13, À14/20, À20/22, À22/0,
À12/12, À25/25, À16/16, À23/26, À16/16, À21/21,
À23/23
À20/20
À23/23
À13/17
À28/28
À22/22
10055
0.0264
À22/21
No. of unique reflections 8560
Rint
6492
0.0737
6979
0.0301
3361
0.0566
9491
0.0424
8347
0.0519
0.0354
Refinement calculations:
full-matrix least-squares on
all F2 values
Weighting expression wa
[s2(Fo2) +
(0.0815P)2
1.3308P)À1
[s2(Fo2) +
(0.0866P)2
1.4188P)À1
429
[s2(Fo2) +
(0.0637P)2
3.6573P)À1
453
[s2(Fo2) +
(0.1303P)2
0.6070P)À1
226
[s2(Fo2) +
[s2(Fo2) +
[s2(Fo2) +
+
+
+
+
(0.0811P)2 + (0.0826P)2 + (0.0999P)2 +
1.8362P)À1
471
7056
1.9646P)À1
482
7371
6.8573P)À1
521
5324
No. of refined parameters 417
No. of F values used
6809
4183
5347
2119
[I 4 2s(I)]
Final R-Indices
R(= S|DF|/S|Fo |)
wR on F2
0.0471
0.1538
0.0549
0.1859
1.054
0.38/À0.30
0.0508
0.1499
1.092
0.49/À0.41
0.0559
0.1882
1.015
0.42/À0.29
0.0495
0.1623
1.070
0.49/À0.44
0.0520
0.1656
1.036
0.37/À0.38
0.0717
0.2407
1.052
0.56/À0.42
S (= goodness of fit on F2) 1.100
Final Drmax/Drmin/e AÀ3 0.38/À0.35
a
2
P = (Fo + 2Fc2)/3.
Table 2 Relevant conformational parameters of the compounds studied
Compound
1a
1b
2a
3a
3b
4a
5a
Torsion anglesa
t1
t2
t3
t4
64.8(2)
À18.8(2)
À32.4(2)
36.4(2)
37.2(2)
51.0(2)
58.8(3)
À19.9(4)
À33.2(3)
36.4(3)
41.6(3)
53.6(3)
69.3(2)
19.9(3)
69.8(3)
À55.6(3)
42.2(3)
57.4(3)
55.2(1)
66.4(2)
À13.4(2)
34.9(2)
À31.7(2)
38.2(2)
59.3(2)
74.6(2)
À19.4(2)
41.6(2)
À31.7(2)
56.2(2)
71.2(2)
63.9(4)
5.8(5)
À73.5(4)
À61.8(4)
49.7(4)
54.3(4)
À32.5(2)
À78.8(3)
À78.8(3)
50.4(3)
t5
t6
50.4(3)
Bond lengths
C(1)–O(1)
C(1)–C(2)
C(2)–C(3)
C(3)–C(4)
C(4)–C(5)
C(5)–C(6)
C(6)–C(1)
C(4)–N(1)
C(4)–N(5)
1.279(2)
1.453(2)
1.389(2)
1.385(2)
1.386(2)
1.390(2)
1.446(2)
1.456(2)
1.278(3)
1.451(3)
1.387(3)
1.395(3)
1.384(3)
1.387(3)
1.454(3)
1.461(3)
1.288(2)
1.437(3)
1.386(3)
1.390(3)
1.377(3)
1.388(3)
1.439(3)
1.460(2)
1.268(3)
1.438(2)
1.382(3)
1.377(2)
1.377(2)
1.382(3)
1.438(2)
1.280(2)
1.450(2)
1.389(2)
1.387(2)
1.384(2)
1.388(2)
1.448(2)
1.458(2)
1.290(2)
1.441(2)
1.389(2)
1.383(2)
1.384(2)
1.395(2)
1.447(2)
1.460(2)
1.307(4)
1.431(4)
1.391(4)
1.389(4)
1.384(4)
1.389(4)
1.429(4)
1.453(4)
1.462(3)
a
For specification of t1–t6 see Scheme 4.
This twisted conformation may obstruct effective resonance
Relating to the stereoisomerism as discussed below, the
between the p-electron systems of the two connected rings.
naphthyl moieties of 5 are in an anti conformation with
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Table 3 Relevant hydrogen bond parameters in the crystal structures of the compounds studied
Atoms involved
Distance
Angle
D-HÁ Á ÁA
1a
DÁ Á ÁA
HÁ Á ÁA
D-HÁ Á ÁA
Symmetry
O(1G)–H(1G)Á Á ÁO(1)
C(17)–H(17)Á Á ÁO(1)
C(13)–H(13)Á Á ÁO(1G)
C(41)–H(41)Á Á ÁO(1G)
C(35)–H(35)Á Á ÁC(24)a
1b
x, y, z
2.732(2)
3.249(2)
3.456(2)
3.475(2)
3.355(2)
1.90
2.33
2.57
2.64
2.60
173
163
155
146
137
1.5 À x, 0.5 + y, 0.5 À z
0.5 + x, 0.5 À y, À0.5 + z
0.5 + x, 0.5 À y, À0.5 + z
1.5 À x, 0.5 + y, 0.5 À z
O(1G)–H(1G)Á Á ÁO(1)
C(17)–H(17)Á Á ÁO(1)
2a
x, y, z
1.5 À x, 0.5 + y, 0.5 À z
2.752(3)
3.208(3)
1.91
2.38
177
145
O(1H)–H(1H)Á Á ÁO(1)
O(1G)–H(1G)Á Á ÁO(1H)
C(8)–H(8)Á Á ÁO(1)
C(24A)–H(24E)Á Á Ácentroid(ring VII)b
3a
x, y, z
x, y, z
2.600(2)
2.748(2)
3.477(3)
3.265(3)
1.79
1.93
2.56
2.78
167
178
162
111
1 À x, À0.5 + y, 0.5 À z
x, y, z
C(7)–H(7)Á Á ÁO(1)
C(10)–H(10)Á Á ÁO(1)
O(1P)Á Á ÁO(1P)
Àz, 1 À x, 1 À y
3.427(4)
3.388(4)
2.252(4)
2.62
2.48
145
166
Àz, 1 À x, 1 À y
0.5 À x, 0.5 + z, 0.5 À y
3b
O(1G)–H(1G)Á Á ÁO(1)
C(13)–H(13)Á Á ÁO(1)
C(37)–H(37)Á Á ÁO(1G)
C(13)–H(13)Á Á ÁO(1G)
4a
x, y, z
2.701(4)
3.263(2)
3.371(3)
3.397(4)
1.89
2.38
2.52
2.69
161
154
150
132
Àx, 0.5 + y, 0.5 À z
x, 0.5 À y, 0.5 + z
Àx, 0.5 + y, 0.5 À z
O(1H)–H(1H)Á Á ÁO(1)
C(13)–H(13)Á Á ÁO(1)
C(8)–H(8)Á Á ÁO(1)
O(1G)–H(1G)Á Á ÁO(1H)
O(1G)–H(1G)Á Á ÁO(1HA)
C(5)–H(5)Á Á ÁO(1G)
5a
x, y, z
2.653(6)
3.382(2)
3.249(2)
2.736(5)
2.894(5)
3.511(2)
1.82
2.43
2.40
1.92
2.08
2.69
171
176
148
165
163
145
1.5 À x, À0.5 + y, 1.5 À z
1.5 À x, À0.5 + y, 1.5 À z
x, y, z
x, y, z
1.5 À x, À0.5 + y, 1.5 À z
O(1G)–H(1G)Á Á ÁO(1)
O(1F)–H(1F)Á Á ÁO(1)
O(1H)–H(1H)Á Á ÁO(1G)
C(43)–H(43)Á Á ÁO(1F)
C(13)–H(13)Á Á ÁO(1F)
C(3)–H(3)Á Á ÁC(21)a
C(33)–H(33)Á Á ÁC(20)a
C(40)–H(40)Á Á ÁC(15)a
C(49)–H(49)Á Á ÁC(19)a
x, y, z
x, y, z
x, y, z
2.615(4)
2.733(4)
2.728(4)
3.273(4)
3.389(4)
3.642(5)
3.657(5)
3.559(5)
3.513(5)
1.78
1.90
2.10
2.54
2.45
2.74
2.78
2.61
2.78
175
173
132
134
171
160
154
176
135
1 À x, À0.5 + y, 1.5 À z
x, 0.5 À y, À0.5 + z
x, 0.5 À y, À0.5 + z
2 À x, 0.5 + y, 1.5 À z
x, 0.5 À y, 0.5 + z
x, 0.5 À y, À0.5 + z
a
b
In order to gain reasonable H-bond geometries, ring carbon atoms instead of ring centroids were chosen as acceptor positions. Means the
centre of the corresponding ring.
Crystallization of 1 from ethanol yielded a solvated complex
1a [1ÁEtOH (1 : 1)] as dark blue crystals. The asymmetric part
of the unit cell contains one dye molecule and one molecule of
ethanol (Fig. 1). As expected, the two components of the
solvated complex 1a are linked by a short O–HÁ Á ÁOÀ hydrogen
bond [d(H(1G)Á Á ÁO(1) 1.90 A].33 The main fragment of the
molecule, given by the aromatic rings I–III, deviates 6.81 from
a linear arrangement, possibly due to packing effects. From
the packing structure of 1a, which is depicted in Fig. 2, it is
apparent that the hydrogen bonded complexes are stacked
along the crystallographic a-axis. Each stack is constructed of
dimers of antiparallel arranged dye molecules with a significant
overlap of their aromatic rings II and III. The shortest
distance between adjacent aryl rings is 3.23 A, suggesting
pÁ Á Áp interaction.34 A close packing structure is realized by
Scheme 3 Specification of torsion angles and numbering of ring
nesting of molecules of neighbouring stacks which allows
components of the betaine molecules 1–5.
intermolecular C–HÁ Á Áp arene contacts [C(35)–H(35)Á Á ÁC(24)
reference to each other, just as the tolyl groups in the
2.60 A, 1371].35 The ethanol molecules are accommodated in
lattice voids, each created by phenyl groups of six dye
structures of the betaines 2 and 3.
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parameters and conformational features of the dye molecule
1a and 1b (see Table 1 and 2). Although the molecular
assemblies of both structures appear identical, the enhanced
steric demand of the alcoholic guest induces a larger molecular
distance along the stacking axis, as well as a disruption of
C–HÁ Á Áp arene contacts between molecules of neighbouring
stacks. Besides face-to-face arene contacts (centroid-to-
centroid: 3.67 A), there are only weak dispersive interactions
between the dye molecules that stabilize the crystal structure.
Crystallization of the betaine dye 2 from methanol gives the
solvated complex 2a with the betaine : solvent stoichiometric
ratio of 1 : 2. The stoichiometric unit of the complex is
presented in Fig. 3. The close distance of one of two disordered
positions of the methyl group (site occupancy factors, SOF:
0.81, 0.19) attached to ring VII indicates an intramolecular
C–H(methyl)Á Á Áp interaction [d(C(24A)Á Á Ácentroid(ring VII)
3.265 A].37 One of the methanol molecules is associated
through a conventional O–HÁ Á ÁO hydrogen bond to the
phenolate oxygen of the host [O(1H)–H(1H)Á Á ÁO(1) 1.79 A,
1671], whereas the hydroxy hydrogen of the second alcohol
molecule
is
involved
in
guest–guest
interaction
[O(1G)–H(1G)Á Á ÁO(1H) 1.93 A, 1781]. Moreover, the acceptor
site O(1G) of this guest is associated with the arene hydrogen
H(3) of a neighbouring dye molecule, so that the crystal
Fig. 1 Perspective view of the stoichiometric unit of solvent complex
1a with the atom numbering scheme. The thermal displacement
ellipsoids of the non-hydrogen atoms are drawn at the 40% probability
level. The broken line represents a hydrogen bond.
Fig. 2 Packing diagram of 1a viewed down the crystallographic
a-axis. The dye molecules are displayed in stick style, solvent molecules
in ball-and-stick style. All hydrogen atoms of the betaine molecule are
omitted for clarity. Broken lines indicate H bond interactions.
Fig. 3 Perspective view of the stoichiometric unit of solvent complex
2a with the atom numbering scheme. The thermal displacement
ellipsoids of the non-hydrogen atoms are drawn at the 40%
probability level. The single broken lines represent conventional
O–HÁ Á ÁO hydrogen bonds, the double broken line indicates a weak
C–HÁ Á ÁO contact.
molecules. Hence, the compound 1a can be described as a
co-ordination-type clathrate36 with pocket style topology.
A structural situation similar to 1a is found in the complex
1b [1Ái-PrOH (1 : 1)], which is obvious from crystallographic
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Fig. 4 Packing diagram of 2a viewed down the crystallographic
a-axis. The dye molecules are displayed in stick style, solvent molecules
in ball-and-stick style. All hydrogen atoms of the betaine molecule are
omitted for clarity. Broken lines indicate H-bond interactions.
Fig. 5 Perspective view of the stoichiometric unit of solvent complex
3a. The unique non-hydrogen positions are labelled. Only one of the
disordered positions of the alcohol molecule is displayed for clarity.
The thermal displacement ellipsoids of the non-hydrogen atoms are
drawn at the 40% probability level.
structure of 2a is composed of infinite chain-like dye–solvent
aggregates running along the crystallographic b-axis (Fig. 4).
This type of interaction and a variety of weaker edge-to-face
arene contacts34 exist between the dye molecules of neighbouring
strands.
On crystallization of the betaine dye 3 from isopropanol,
blue prisms were obtained which turned out to be a solvated
complex 3a [3ÁiPrOH (1 : 1)]. Because of the crystallographically
imposed two-fold symmetry, the asymmetric unit cell contains
one half of the dye molecule and one half of the isopropanol
(Fig. 5). All phenyl rings and the phenolate ring of the dye
molecule are planar within the experimental errors, while the
pyridinium ring is slightly twisted around its N(5)Á Á ÁC(8) axis.
Interestingly enough, there is no H-bond connection between
the dye molecule and the alcohol. Instead, each phenolate
oxygen O(1) is connected to two symmetry-related dye
molecules via a bifurcated C–HÁ Á ÁO contact38 (Table 3). The
packing arrangement of 3a (Fig. 6) seems to be further
stabilized by a complicated pattern of edge-to-face and stacking
interactions34,39 between the peripheral aromatic rings. On the
other hand, although we were not able to localize the hydroxy
hydrogen of the i-PrOH molecule, the OÁ Á ÁO distance of
2.25 A between adjacent alcoholic oxygens suggests hydrogen
bond interactions between them, creating trimeric alcohol
associates (Fig. 6) which are located in channel-like cavities
extending along the three-fold symmetry axis of the crystal. It
should be noted that the high mobility of the alcohol molecules
can also be observed at low temperatures (93 K). Obviously,
the tight interlocking of dye molecules creates a rigid host
lattice structure with channels that show characteristic widenings
with a maximum diameter of approximately 10.6 A around the
trimeric alcohol entities and empty spaces along the channel
axis. Accordingly, the structure of 3a is more likely to be
termed a ‘‘true clathrate’’40 with a channel-like topology.
Fig. 6 Packing diagram of 3a. All hydrogen atoms are omitted for
clarity. Broken lines indicate short OÁ Á ÁO distances, suggesting
H-bond interactions.
Unlike 3a, crystallization of 3 from n-BuOH yields the
solvated 1 : 1 complex 3b, in which the disordered solvent
molecule (SOF 0.79, 0.21) is associated in the familiar way
to the phenolate oxygen of the dye molecule. The mode of
non-covalent interactions in the crystal structure of 3b, which
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Fig. 7 Structure motif of the solvent complex 3b. Only one of the disordered positions of the alcohol molecule is displayed for clarity. Molecules
drawn in bold style represent the content of the asymmetric cell unit. Broken single lines indicate hydrogen bonds; face-to-face arene interactions
are marked by broken double lines.
is illustrated in Fig. 7, comprises C–HÁ Á ÁO hydrogen bonds
[d(HÁ Á ÁO) 2.51, 2.69 A] and face-to-face interactions between
aromatic rings II and III of symmetry related host molecules.
The betaine dye molecule 4 represents the para-methylated
analogue of 1, but yields a 1 : 2 solvent complex when crystallized
from ethanol. The asymmetric part of the unit cell contains
one betaine dye molecule and two molecules of the solvent,
one of the latter ones disordered on two sites (SOF: 0.74 and
0.26). Consequently, a comparative consideration of the
crystal structures 1a and 4a reveals different patterns of
non-covalent interactions. In 4a, one of the alcohol molecules
is associated via O–HÁ Á ÁO hydrogen bonding with a dye
molecule [O(1H)–H(1H)Á Á ÁO(1) 1.82 A, 1711], while its oxygen
O(1H) is linked to the second solvent molecule
[O(1G)–H(1G)Á Á ÁO(1H) 1.92 A, 1651] (Fig. 8). Furthermore,
the phenolate oxygen O(1) is involved in relatively short
C–HÁ Á ÁO hydrogen bonds to an adjacent dye molecule
[d(HÁ Á ÁO) 2.40, 2.43 A]. The differences regarding the crystal
structures of 1a (Fig. 2) and 4a (Fig. 8) are also evident from
the lattice structures of the dye molecules, as well as the
locations of the solvent molecules.
contributing to the nearly co-planar geometry of this building
unit. The overall geometry of the dye molecule deviates only
slightly from C2-symmetry. The packing arrangement of 5a
(Fig. 9) is also characterized by a variety of areneÁ Á Áarene
interactions.34,39 Some additional intermolecular distances
indicate potential weak C–HÁ Á Áp contacts35 between naphthyl
moieties, arranged in the crystal in a tilted edge-to-face mode
with 2.61 o d(HÁ Á Áp) o 2.79 A (Table 3). Furthermore, a
naphthyl moiety and the electron-deficient pyridinium ring of
an adjacent dye molecule, which are nearly parallel to each
other, have a centroidÁ Á Ácentroid distance of 4.65 A, possibly
suggesting a weak pÁ Á Áp interaction.
Stereoisomerism of compounds 9d and 5
1
The H and 13C NMR spectra of compound 9d obtained in
[D2]tetrachloroethane (TClE) at T = 20 1C show the presence
of two isomeric forms in an approximately 50 : 50 mixture
owing to restricted rotation about the naphthyl–nitrophenol
bond. Hence, these two atropisomeric stereoisomers of 9d
correspond to the meso compound and the racemic mixture
of the enantiomers (Scheme 4). Variable temperature NMR
analysis revealed line shape changes in proton signals and
collapse of split carbon signals determined in the temperature
range between 20 and 60 1C. While the 13C NMR of compound
9d in [D2]TClE solution at 20 1C shows a total of 24 signals, a
consecutive decrease to 14 signals (expected number of signals
for free bond rotation) was observed in the course of the
temperature increase (see Experimental). This study allows us
to estimate the coalescence temperature for free rotation of the
naphthyl–nitrophenol bond as around 55 1C, corresponding to
a rotational barrier of about 16.9(5) kcal molÀ1. A rather
similar conformational behaviour based on NMR data in
C6D6 solution, that is a barrier to naphthyl rotation of
Crystallization of the naphthyl-substituted dye molecule 5
from methanol yielded dark coloured blocks of a solvated
complex 5a [5ÁMeOH (1 : 3)]. The asymmetric part of the unit
cell contains one betaine dye molecule and three molecules of
the solvent (Fig. 9). The phenolate oxygen O(1) is connected
with two methanol molecules via hydrogen bonds
[O(1G)–H(1G)Á Á ÁO(1) 1.78 A, 1751, O(1F)–H(1F)Á Á ÁO(1)
1.90 A, 172.61], whereas the remaining alcohol molecule is
H-bonded to the oxygen of MeOH 2 [O(1H)–H(1H)Á Á ÁO(1G)
2.10 A, 1321]. Moreover, the O atom of MeOH 1 is involved in
two relatively short C–HÁÁÁO contacts37 including aryl hydrogens
of rings II and III of the nearest betaine molecule, hence
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Fig. 8 Structure motif of the solvent complex 4a. Only one of the disordered positions of the alcohol molecule 1 is displayed for clarity. Molecules
drawn in bold style represent the content of the asymmetric cell unit. Broken single lines indicate hydrogen bonds; face-to-face arene interactions
are marked by broken double lines.
Fig. 9 Structure motif of the solvent complex 5a. Molecules drawn in bold style represent the content of the asymmetric unit cell. Broken single
lines indicate hydrogen bonds; face-to-face arene interactions are marked by broken double lines.
18.0 kcal molÀ1 at 67 1C, has previously been reported for the
parent compound 2,6-bis(1-naphthyl)phenol lacking the
p-nitro group.41
The somewhat increased rotational barrier found for the
parent phenol molecule is very likely attributable to both
Scheme 4 Rotational isomerism of compound 9d.
the different solvents used for the NMR determinations and
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Table 4 Vis. absorption maxima (lmax, nm) of diluted solutions (10À3 M) of the betaine dyes 2–5, measured in solvents of different polarity at
room temperature (25 1C) with corresponding ET values (kcal molÀ1)a, including ET(30) values
1
2
3
4
5
(ET 30)b
lmax (ET)
lmax (ET)
lmax (ET)
lmax (ET)
Solvent
Methanol
Ethanol
1-Butanol
2-Propanol
Dichloromethane
(55.4)
(51.9)
(49.7)
(48.4)
(40.7)
496 (57.6)
540 (52.9)
567 (50.4)
584 (48.9)
690 (41.4)
516 (55.4)
554 (51.6)
580 (49.3)
600 (47.7)
708 (40.4)
521 (54.9)
558 (51.2)
582 (49.1)
602 (47.5)
714 (40.0)
504 (56.7)
541 (52.8)
566 (50.5)
585 (48.9)
681 (42.0)
a
b
Calculated according to ref. 14. Taken from ref. 5.
the additional nitro substituent in the case of 9d. However,
coming to a clear decision on the real consequences of these
facts is a problem. A previous study has shown that o-phenyl-
phenols remain monomeric in solution with strong evidence for
p-hydrogen bonding between the OH proton and an o-phenyl
ring.42 Hence, measurement of the rotational barrier should be
affected by the polarity and hydrogen bond acceptor ability of
the solvent. On the other hand, one should expect an increase of
the OH acidity caused by the nitro group of 9d having an
influence on the intramolecular p-hydrogen bonding and, thus,
being connected with the rotational flexibility of the molecule.
A conformational behaviour similar to the nitrophenol 9d
was observed for the betaine 5, featuring a corresponding
structural situation for the two 1-naphthyl units of the
molecule. But, due to the betaine structure of 5, the O atom
refers now to an anionic phenolate oxygen instead of the
hydroxyl group of 9d. From this angle, the rotational barrier
of the naphthyl–nitrophenolate bond of 5 is expected to be
somewhat lower compared to 9d, since p-hydrogen bonding
cannot produce an effect. However, owing to the neighbouring
phenyl residues of the pyridinium moiety, an additional steric
hindrance may become effective.6 Putting it in concrete terms,
the atropical stereoisomerism of the compound 5 is becoming
the new betaine dyes 2–5 in various solvents of different
polarity have been determined. These data, together with the
corresponding electronic transition energies ET(2)–ET(5) in
kcal molÀ1, are listed in Table 4. In analogy to the prior
standard betaine dye 1,5 included in Table 4, the new dyes 2–5
also exhibit an extraordinary negative solvatochromism. In
changing the solvent from polar methanol to less polar
dichloromethane, the hypsochromic shifts (Dlmax) of the
intramolecular CT absorption band range between À177 and
À194 nm, dependent on the respective dye. This corresponds
to an increase of their molar transition energies ET of between
14.7 and 16.2 kcal molÀ1. At a rough estimate, these values are
similar to those found for 15 and related alkyl substituted
derivatives of 1.14 At most, the o-tolyl and 1-naphthyl derivatives
(2 and 5, respectively) behave a little different regarding the
hypsochromic shifts and DET, as compared with the other
betaines, which is possibly a consequence of the steric conditions
owing to these particular substituents. Actually, in detail, there
are other differences between the individual compounds the
causes of which are difficult to explain, however. Nevertheless,
it is shown that with increasing solvent polarity, the high
dipolar ground state of the new betaine dyes 2–5 is increasingly
stabilized by differential solvation, relative to the less dipolar
CT excited state, with the observed hypsochromic band shift
as consequence.
1
apparent in a split of signals both in the H and 13C NMR
spectra in [D2]TClE at 20 1C with line shape changes and
consecutive decrease of signals on temperature increase. At
20 1C, the 13C NMR spectrum shows 45 signals that collapsed
to 22 resolved signals at 80 1C (25 individual signals expected
for free rotation of the molecule). The four carbon signals
ranging between 157 and 158 ppm, assigned to the 1-PhO
C-atom,14,43 suggests the presence of four atropisomeric
species at 20 1C, while a singlet at 157.7 ppm is observed at
80 1C, indicating rapid interconversion of the atropisomers.
We can therefore estimate that the barrier to free rotation in 5
is higher than the value of 16.0 kcal molÀ1 at 55 1C measured
for the related nitrophenol 9d. Considering a coalescence
temperature for the betaine 5 around 75 1C, the corresponding
rotational barrier is about 18.1(5) kcal molÀ1. Analysis of the
crystals obtained from a solution of 5 in methanol by X-ray
diffraction (see above) showed the presence of a particular
chiral form as both enantiomers in the unit cell, featuring the
molecule with naphthyl moieties rotated in an anti orientation
and twisted phenyl groups.
Conclusion
Following the established procedure for the preparation of
para-pyridinium N-phenoxides,4,28,29 four new betaine dyes
2–5 of the Reichardt’s type have been synthesized. They
feature two tolyl substituents in different attachment or two
1-naphthyl groups in the phenoxide moiety, instead of simple
phenyls as for the standard betaine dye 1. Based on the
position of the long wavelength intramolecular charge-transfer
absorption band in solvents of different polarity, the negative
solvatochromism and, thus, the calculated ET-values of the
betaine dyes 2–5 fall between the standard compound 15 and
known related alkyl derivatives of 1.14 Therefore, both the
present modes of methyl substitution and the exchange of
phenyl for 1-naphthyl groups in 1 do not show unusual effects
on the solvatochromatic properties.
From variable-temperature solution NMR measurement,
the betaine 5, as well as the intermediate compound 9d, were
determined to exist as rotational stereoisomers at ambient
temperature and free rotating molecules at increased temperature.
In the crystalline alcoholic complexes of 2–5, as well as the
Solvatochromic properties of the betaine dyes
The positions of the solvatochromic long wavelength intra-
molecular charge-transfer (CT) absorption band (lmax, nm) of
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unsubstituted parent compound 1, i.e. 1a, 1b, 2a, 3a, 3b, 4a
and 5a, the betaine molecules are considerably distorted
around the arene–arene and arene–heteroarene bonds,
preventing significant conjugation. Particularly, in the cases
of 2, 3 and 5, the tolyl and naphthyl moieties are all in an anti
conformation with reference to each other. Moreover, it is
shown by the dihedral angles in the range between 55 and 751,
involving the planes of the phenoxide and pyridinium rings,
that the ground state structures of the present betaines
are genuine zwitterions. This is in agreement with earlier
observations,15,16 but actually conflicting with required mobility
of electron density between the two rings upon excitation,2
being previously discussed along different lines.12,44 However,
it is also not unlikely that the molecular geometries differ
between crystalline and solution state, so as to make normal
p-orbital interaction possible. Nevertheless, in accordance with
previous computer simulation studies,45 it is demonstrated with
the crystal structures of the present solvent complexes, except
3a, that the preferred docking site for the hydrogen donor
alcohol molecules is the phenolate oxygen of the dye molecules.
Generally, the molecular structures in the crystals are rather
similar and not in obvious contrast to previous reports,12,15,16
unlike the packing modes, showing more developed differences
with modification of the lateral aryl groups.
under N2 at room temperature or slightly elevated temperature
for between 20 and 96 h. The solid was filtered off and most of
the solvent removed under reduced pressure. Water was
refilled and conc. hydrochloric acid added until complete
precipitation of the crude phenol. Details including procedure
of purification and data of the individual compounds are
given below.
2,6-Bis(2-methylphenyl)-4-nitrophenol
(9a).
1,3-Bis(2-
methylphenyl)propan-2-one (7a) and (8) were reacted at
30–35 1C for 20 h. Purification by column chromatography
(SiO2, eluent: toluene) yielded 53% colourless crystals; mp
192 1C (lit.50 192–193 1C). IR (KBr): v˜ = 3446 cmÀ1 (s, O–H),
3060, 3012, 2920, 2860 (w, C–H), 1600, 1584 (m, Ar), 1516
1
(s, N–O), 1455, 1380 (m, C–H), 1325 (s, C–NO2). H NMR
(400 MHz, [D6]DMSO): d = 2.16 (s, 6 H, CH3), 7.25–7.37 (m,
8 H, Ar–H), 7.91 (s, 2 H, Ar–H), 9.75 (s, 1 H, OH) ppm.
13C NMR (100 MHz, [D6]DMSO): d = 19.47 (CH3), 125.58,
126.02, 128.27, 129.96, 130.10, 130.19, 136.37, 136.57, 139.41
(C–NO2), 157.73 (C–OH) ppm. MS (GC): m/z = 319 [M]+.
C20H17NO3 (319.36): calcd. C 75.22, H 5.36, N 4.39; found C
75.51, H 5.51, N 4.23%.
2,6-Bis(3-methylphenyl)-4-nitrophenol (9b). 1,3-Bis(3-methyl-
phenyl)propan-2-one (7b) and (8) were reacted at room
temperature for 96 h. The solid which was present immediately
after completion of the reaction was collected and recrystal-
lized from ethanol to yield a first crop of the product. A second
crop was isolated via treatment of the filtrate as specified in
the general procedure, followed by column chromatography
(SiO2, eluent: toluene) to give a total yield of 72% colourless
crystals; mp 146 1C (lit.50 145 1C). IR (KBr): v˜ = 3478 cmÀ1
(s, O–H), 3094, 3060, 3037, 2949, 2917, 2857 (w, C–H), 1609,
1581 (m, Ar), 1524 (s, N–O), 1483, 1375 (m, C–H), 1334
(s, C–NO2). 1H NMR (400 MHz, [D6]DMSO): d = 2.37
(s, 6 H, CH3), 7.23–7.40 (m, 8 H, Ar–H), 8.19 (s, 2 H, Ar–H),
9.89 (s, 1 H, OH) ppm. 13C NMR (100 MHz, [D6]DMSO):
d = 21.12 (CH3), 124.98, 126.51, 128.50, 128.63, 129.96,
131.14, 136.56, 137.74 (Ar), 140.15 (C–NO2), 157.36 (C–OH)
ppm. MS (GC): m/z = 319 [M]+. C20H17NO3 (319.36): calcd.
C 75.22, H 5.36, N 4.39; found C 75.09, H 5.12, N 4.17%.
In addition to the increase of insight in the structural
features of this important compound class, the new betaine
dyes may provide a basis for future quantum chemical
calculations in order to improve the knowledge of the excitation
process.46 Other promising aspects are to use these solvato-
chromic dyes as sorptive transducer elements in optical
chemical sensors9,13,47 or in the development of nonlinear
optical materials.10,48
Experimental
Methods and materials
Melting points: Kofler melting point microscope (uncorrected).
1H and 13C NMR (internal standard TMS): Bruker AVANCE
DPX 400 and AVANCE DPX 500. MS: A.E.I. MS 50, Kratos
FAB-MS Concept 1H, and Hewlett Packard GC-MS 5989
A/5890 II. Elemental analysis: Heraeus CHN rapid analyzer.
TLC-analysis: aluminium sheets precoated with silica gel
60 F254 (Merck). Column chromatography: silica gel
(63–100 mm, Merck). Organic solvents were purified by standard
procedures.49 Compound 1 was purchased from Aldrich.
2,6-Bis(4-methylphenyl)-4-nitrophenol (9c). 1,3-Bis(4-methyl-
phenyl)propan-2-one (7c) and
8 were reacted at room
temperature for 96 h. Purification by column chromatography
(SiO2, eluent: toluene) yielded 80% colourless crystals; mp
136 1C (lit.50 137 1C). IR (KBr): v˜ = 3487 cmÀ1 (s, O–H),
3034, 2920, 2860, (w, C–H), 1613, 1584 (m, Ar), 1505 (s, N–O),
Synthesis
1
1448, 1385 (m, C–H), 1328 (s, C–NO2). H NMR (400 MHz,
[D6]DMSO): d = 2.36 (s, 6 H, CH3), 7.29 (d, 3J = 8 Hz, 4 H,
The starting ketones 7a–7d were synthesized from 6a–d using
two alternative literature procedures (A31 and B32) as specified
in Scheme 2. The data obtained for these compounds (7a,50,51
7b,50,52,53 7c,54–56 7d57,58) correspond with the literature.
The triphenylpyrylium hydrogen sulfate (11)59 and 2-nitro-
malonaldehyde-Na60 (8) were prepared as described.
3
Ar–H), 7.47 (d, J = 8 Hz, 4 H, Ar–H), 7.98 (s, 2 H, Ar–H),
9.83 (s, 1 H, OH) ppm. 13C NMR (100 MHz, [D6]DMSO):
d = 20.86 (CH3), 124.75, 129.61, 129.26, 130.96, 133.73,
137.30 (Ar), 140.13 (C–NO2), 157.49 (C–OH) ppm. MS
(GC): m/z = 319 [M]+. C20H17NO3 (319.36): calcd. C 75.22,
H 5.36, N 4.39; found C 74.90, H 5.37, N 4.34%.
General procedure.30,50 Synthesis of nitrophenols 9a–d. To a
stirred mixture of the respective ketone 7a–d (10 mmol) in
degassed ethanol (6 mL) and THF (6 mL) was added a solution
of 2-nitromalonaldehyde-Na monohydrate (8) (12 mmol) in
aqueous NaOH (1 M, 26 mL). The mixture was kept stirring
2,6-Di(1-naphthyl)-4-nitrophenol (9d). 1,3-Di(1-naphthyl)-
propan-2-one (7d) and 8 were reacted at room temperature
for 48 h. Purification by column chromatography (SiO2,
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eluent: toluene) yielded 61% light yellow crystals; mp 196 1C. IR
(KBr): v˜ = 3493 cmÀ1 (s, O–H), 3053, 2927, 2851 (w, C–H),
1619, 1584 (m, Ar), 1524 (s, N–O), 1448, 1388 (m, C–H) 1328
(s, C–NO2). 1H NMR (400 MHz, [D2]TClE, 20 1C): d = 5.73 (s,
1 H, OH), 7.43–7.66 (m, 10 H, Ar–H), 7.88–7.95 (m, 4 H, Ar–H),
8.27 (s, 2 H, Ar–H) ppm. 1H NMR (400 [D2]TClE, 60 1C): d =
5.64 (s, 1 H, OH), 7.40–7.80 (m, 1 OH, Ar–H), 7.80–8.00 (m, 4 H,
Ar–H), 8.30 (s, 2 H, Ar–H). 13C NMR (100 MHz, [D2]TClE,
20 1C): d = 125.3, 125.4, 126.00, 126.04, 126.9, 127.34, 127.36,
127.4, 128.1, 128.2, 128.6, 128.7, 129.0, 129.1, 129.9, 131.5, 131.6,
132.6, 132.7, 134.0 (Ar), 141.3, 141.4 (C–NO2) 156.8, 156.9
(C–OH) ppm. 13C NMR (100 MHz, [D2]TClE, 60 1C):
d = 125.3, 126.0, 126.8, 127.3, 127.4, 128.3, 128.6, 129.0,
129.9, 131.8, 132.8, 134.2 (Ar), 141.6 (C–NO2), 156.8 (C–OH)
ppm. MS (GC): m/z = 391 [M]+. C26H17NO3 (391.42): calcd. C
79.78, H 4.38, N 3.58; found C 79.32, H 4.31, N 3.40%.
2863 cmÀ1 (w, C–H), 1616, 1597 (s, Ar), 1461, 1356 (s, C–H).
1H NMR (400 MHz, CDCl3): d = 2.28 (s, 6 H, CH3), 6.40
(s, 2 H, Ar–H), 6.90 (d, J = 7.4 Hz, 2 H, Ar–H), 6.95–7.10
3
(m, 6 H, Ar–H), 7.25–7.40 (m, 10 H, Ar–H), 7.55–7.65 (m, 3 H,
Ar–H), 7.80–7.90 (m, 2 H, Ar–H), 8.05 (s, 2 H, Py-H) ppm.
13C NMR (100 MHz, CDCl3): d = 21.39 (CH3), 117.93,
125.30, 125.51, 125.83, 126.34, 127.60, 127.68, 128.74,
129.10, 129.59, 129.81, 130.11, 132.05, 133.68, 134.02,
135.98, 140.37, 153.50 (Ar, 3,4,5-Py), 156.36 (2,6-Py), 169.10
(1-PhO) ppm. MS (FAB): m/z = 580.2. [M]+. C43H33NOÁ
2H2O (615.28): calcd. C 83.87, H 6.06, N 2.27; found: C
83.39, H 5.84, N 2.26%.
2,6-Bis(4-methylphenyl)-4-(2,4,6-triphenyl-1-pyridinio)phenolate
(4). From aminophenol 10c and 11 in 43% yield as a blue
solid; mp 200 1C. IR (KBr): v˜ = 3056, 3025, 2917, 2860 cmÀ1
(w, C–H), 1622, 1597 (s, Ar), 1492, 1397, 1356 (s, C–H).
1H NMR (400 MHz, CDCl3): d = 2.28 (s, 6 H, CH3), 6.51
General procedure.61 Synthesis of aminophenols 10a–d. A
suspension of the corresponding nitrophenol 9a–d (2.5 mmol)
and of 10% Pd/C (50 mg) in dry ethanol (25 mL) was
hydrogenated in a Parr apparatus at 2 atm and at room
temperature for 5 h. The catalyst was filtered off under argon
and the product solution containing 10a–d, respectively, was
directly used in order to avoid oxidation decomposition of
the compounds. Evaporation of a sample showed complete
reaction (TLC analysis).
3
(s, 2 H, Ar–H), 7.00 (d, J = 7.4 Hz, 2 H, Ar–H), 7.20–7.30
(m, 7 H, Ar–H), 7.35–7.50 (m, 8 H, Ar–H), 7.60–7.65 (m, 4 H,
Ar–H), 7.80–7.90 (m, 2 H, Ar–H), 8.04 (s, 2 H, Py-H) ppm.
13C NMR (100 MHz, [D6]DMSO): d = 20.77 (CH3), 125.04,
128.16, 128.66, 128.72, 128.78, 128.89, 129.25, 129.53, 129.87,
130.10, 132.45, 133.53, 133.69, 134.76, 136.27, 144.53, 154.86
(Ar, 3,4,5-Py), 156.66 (2,6-Py), 164.83 (1-PhO) ppm. MS
(HR): m/z = 579.2538 [M]+. C43H33NOÁ2H2O (615.28):
calcd. C 83.87, H 6.06, N 2.27; found: C 83.14, H 6.02,
N 2.16%.
General procedure.29 Synthesis of the betaine dyes 2–5. To
the above solutions of the corresponding aminophenol 10a–d
(2.5 mmol) in EtOH were added under Ar 2,4,6-triphenyl-
pyrylium hydrogensulfate (11) (1.0 g, 2.5 mmol) and anhydrous
sodium acetate (1.0 g, 12 mmol). The mixture was heated to
reflux for 3 h. Then, 5% aqueous NaOH solution (7.5 mL) was
added to the hot solution. The major part of EtOH is removed
under reduced pressure, refilled with water, condensed again
and so on until complete precipitation of the betaine. The
precipitate was collected, washed with water and purified by
column chromatography (SiO2, eluent: EtOH). Details and
data of the individual compounds are given below.
2,6-Di(1-naphthyl)-4-(2,4,6-triphenyl-1-pyridinio)phenolate
(5). From aminophenol 10d and 11 in 56% yield as a blue
solid; mp 4 300 1C. IR (KBr): v˜ = 3050, 3003 cmÀ1 (w, Ar),
1619, 1594 (s, Ar). 1H NMR (500 MHz, [D2]TClE, 20 1C):
d = 6.63, 6.65, 6.83, 6.85, 7.00, 7.03, 7.12, 7.14 (6 H, Ar–H),
7.27–7.69 (m, 16 H, Ar–H), 7.82–7.90 (m, 6 H, Ar–H), 8.18
1
(s, 2 H, Py-H) ppm. H NMR (500 MHz, [D2]TClE, 80 1C):
d = 6.82 (s, 2 H, Ar–H), 6.96 (s, 2 H, Ar–H), 7.06, 7.13–7.39
(d, 2 H, Ar–H), 7.32–7.66 (m, 16 H, Ar–H), 7.83–7.95 (m, 6 H,
Ar–H), 8.19 (s, 2 H, Py-H) ppm. 13C NMR (125 MHz,
[D2]TClE, 20 1C): d = 123.8–134.0 (39 signals, Ar, 3,4,5-Py,
2,3,4,5,6-PhO) 152.46, 152.52 (2,6-Py), 157.3, 157.5, 157.7,
158.0 (1-PhO) ppm. 13C NMR (125 MHz, [D2]TClE, 80 1C):
d = 125.0, 125,7, 126.2, 126.6, 127.0, 127.9, 128.4, 128.7,
128.9, 129.6, 130.2, 130.5, 130.8, 131.2, 131.8, 132.5, 132.8,
133.5, 134.2, 134.3 (Ar, 3,4,5-Py, 2,3,4,5,6-PhO), 152.3
(2,6-Py), 157.7 (1-PhO) ppm. MS (HR): m/z = 651.2560
[M]+. C49H33NOÁH2O (669.27): calcd. C 87.86, H 5.27,
N 2.09; found: C 87.93, H 5.40, N 1.94%.
2,6-Bis(2-methylphenyl)-4-(2,4,6-triphenyl-1-pyridinio)phenolate
(2). From aminophenol 10a and 11 in 35% yield as a blue
solid; mp 218 1C. IR (KBr): v˜ = 3053, 3015, 2952 cmÀ1 (w,
C–H), 1619, 1597 (s, Ar), 1473, 1359 (s, C–H). 1H NMR
(400 MHz, CDCl3): d = 2.05 (s, 6 H, CH3), 6.37 (s, 3 H,
3
Ar–H), 6.72 (d, J = 6.9 Hz, 2 H, Ar–H), 6.90–7.10 (m, 5 H,
Ar–H), 7.26 (s, 3 H, Ar–H), 7.30–7.50 (m, 8 H, Ar–H),
7.55–7.65 (m, 3 H, Ar–H), 7.85 (d, 3J = 6.8 Hz, 1 H,
Ar–H), 8.06 (s, 2 H, Py-H) ppm. 13C NMR (100 MHz,
CDCl3): d = 20.32 (CH3), 124.18, 125.97, 126.62, 127.36,
128.02, 129.51, 130.09, 130.27, 131.01, 131.25, 131.71, 132.00,
133.21, 133.72, 135.53, 135.66, 138.52, 142.09, 157.20 (Ar,
3,4,5-Py, 2,3,4,5,6-PhO), 158.96, (2,6-Py) 165.22 (1-PhO)
ppm. MS (HR): m/z = 579.2543 [M]+. C43H33NOÁH2O
(597.27): calcd. C 86.40, H 5.90, N 2.34; found: C 85.93,
H 5.94, N 2.14%.
Crystallography
Crystals of the complexes suitable for single crystal X-ray
diffraction studies were obtained by slow solvent evaporation
of solutions of the respective betaine dyes in the corresponding
solvent. Information concerning the crystallographic data and
the structure refinement calculations of the three compounds is
summarized in Table 1. Data collection of 1a, 1b, 2a, 3b, 4a
and 5a was carried out on a Kappa APEX II diffractometer
(Bruker AXS), using o- and f-scans. The collected data were
corrected for Lorentz and polarisation effects. The structures
2,6-Bis(3-methylphenyl)-4-(2,4,6-triphenyl-1-pyridinio)phenolate
(3). From aminophenol 10b and 11 in 54% yield as a
blue solid; mp 121–124 1C. IR (KBr): v˜ = 3056, 3028, 2917,
ꢀc
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were solved by direct methods62 and refined by full-matrix
least squares calculations on F2.63 The non-hydrogen positions
and disorder sites were refined together with their anisotropic
displacement parameters, and the H atoms and H disorder
sites were treated isotropically. All H positions were held
riding on the respective parent O or C atoms during the
subsequent calculations. Data of 3a were collected on a
Enraf-Nonius CAD-4 diffractometer. Crystals of 3a turned
out to show weak scattering power which allowed data
collection up to a Y-value of 651. The cell parameters were
determined and refined using the CAD4-Express program.64
Two standard reflections, monitored every 120 min, showed
a crystal decay of 13% during the entire data collection
procedure. Reflection data were corrected for Lorentz and
polarization effects using the XCAD4 program.65 The structures
were solved by application of direct methods,62 and refined by
full-matrix least-squares calculations on F2 with anisotropic
vibration displacement parameters for all non-hydrogen atom
positions.63 All carbon-bonded H atoms were given positions
calculated using geometric evidence, whereas the hydroxyl
hydrogen could not be located from a difference electron
density map.
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Acknowledgements
Financial support by the Deutsche Forschungsgemeinschaft
(DFG) and the Fonds der Chemischen Industrie is gratefully
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