Mesomorphic di- and tetra-fluorinated imines and their complexes with Re I

Article abstract of DOI:10.1039/a802167h

The synthesis of some di- and tetra-fluoro imine mesogens is described and their mesomorphism is compared with that of the parent, unfluorinated materials. The comparison reveals that in the fluorinated compounds, more ordered smectic phases were suppress

Full text of DOI:10.1039/a802167h

J O U R N A L O F
Mesomorphic di- and tetra-fluorinated imines and their complexes
with ReI
Xiao-Hua Liu,a,b Ian Manners*b and Duncan W. Bruce*a†
aDepartment of Chemistry, University of Exeter, Stocker Road, Exeter, UK EX4 4QD
bDepartment of Chemistry, University of T oronto, T oronto, M5S 3H6, Canada
C H E M I S T R Y
The synthesis of some di- and tetra-fluoro imine mesogens is described and their mesomorphism is compared with that of the
parent, unfluorinated materials. The comparison reveals that in the fluorinated compounds, more ordered smectic phases were
suppressed and crystal phases were destabilised; nematic phases were uniformly destabilised. The imines were then reacted with
[ReMe(CO) ] to give related orthometallated complexes which were also mesomorphic.
5
fully illustrated by the work of the Hull group with substituted
Introduction
terphenyls.5 From all of these studies, it is clear that a subtle
combination of steric and electronic effects acts to determine
the resulting mesomorphism.
In low molar mass liquid crystalline systems, fluoro-substi-
tution has been known since 1925.1 Fluorine has the smallest
van der Waals’ radius of any substituent other than hydrogen
Lateral fluorination has also been studied in low molar mass
metallomesogens. For example, the central core of stilbazole
silver() complexes was modified by introduction of lateral
fluoro-substituents into complexes with triflate and dodecyl
sulfate counter ions.6 Depending on the position of the fluoro
substituent, the mesomorphic behaviour is affected in a differ-
ent way. When the fluoro substituents occupy position 3 of
the aromatic rings (Fig. 2) nematic phases are formed less
frequently or even suppressed totally, melting points are
decreased, and smectic C phases are destabilised, resulting in
a pronounced widening of the smectic A phases in comparison
with their non-substituted stilbazole silver() complexes.
Further, the cubic phase seen in the parent complexes is now
absent. However, when the fluoro substituents occupy position
2, different effects are observed; the clearing points are signifi-
cantly depressed and melting points are also decreased, but to
a lesser extent. The smectic C phase is stabilised at the total
expense of the smectic A phase, the nematic phase is promoted
and for X=C H OSO , cubic phases are retained. Imrie and
˚
˚
(F=1.47 A, H=1.2 A)2 and it also has highest electronegativity
of any element. Fluorine can, therefore, exert appreciable
electronic effects and yet, because of its small size, its effect on
the close packing of the molecules is less than any other
substituent. The effect of fluorination in mesogens has been
well documented3 and several general conclusions can be
drawn from investigations carried out on calamitic systems.
Lateral fluoro substitution in low molar mass systems has
varied effects and critically depends on the position at which
the fluoro substituent is introduced.4 Fig. 1 shows the transition
temperatures for a parent compound and also for two of its
mono-fluorinated derivatives. It can be seen that the 2-fluoro
derivative (fluorine positioned centrally) has reduced nematic
character compared with the parent system, while when the
fluoro substituent is positioned near the end of core unit (3-
fluoro derivative), nematic character has been eliminated and
smectic phase stability has been enhanced. Both of the fluori-
nated compounds have a lower melting point than the parent
system.
12 25
3
coworkers7 have reported a difluoro-substituted ferrocene met-
allomesogen (Fig. 3), and here, fluoro substitution led to lower
temperature mesogens. Fluorination has also been studied in,
for example, complexes of salicylaldimates,8 salen,9 dithioben-
zoates10 and b-diketonates.11
O
O
X
Y
C6H13
O
C5H11
As part of our studies on calamitic metallomesogens contain-
ing octahedral metal centres,12 we have studied orthometallated
X
Y
H H Crys • 50 • N • 63 • I
Crys • 28 • N • 37 • I
H F Crys • 40 • SA • 49 • I
F
H
F
2
3
OCnH2n + 1
+
Ag
N
N
Fig. 1 Example of the dependence of transition temperatures on
position of fluorination
CnH2n + 1
O
X–
X = OTf, C12H25OSO3
3
2
F
Predicting the effect which lateral fluoro-substitution will
have is, however, difficult because steric factors must be
considered in addition to molecular polarizability.3b,c In most
systems, however, the trends for laterally fluoro-substituted
compounds show similar patterns, depending on their number
and distribution. Positioned so that they contribute to an
‘outboard’ dipole, they have the possibility to stabilise smectic
phases perhaps at the expense of nematic phases, while pos-
itioned to create a net lateral dipole, they can reduce clearing
points and promote nematic phases, often at the expense of
smectic phases (Fig. 1). Some of these effects are rather beauti-
Fig. 2 Laterally fluorinated stilbazole complexes of silver()
O
O
OC8H17
Fe
F
F
Crys • 115 • N • 129 • I
†E-mail: d.bruce@exeter.ac.uk
Fig. 3 Mesomorphic difluoro-substituted ferrocene
J. Mater. Chem., 1998, 8(7), 1555–1560
1555

manganese and rhenium complexes of extended imines.13 In
these systems we typically found that a four-ring imine (e.g.
10) with a clearing point of around 300 °C and more than one
isolated by adding aqueous sodium hydrogen carbonate, acid-
ifying with cold, concentrated hydrochloric acid, and then
extracting with chloroform. After crystallisation from chloro-
form, compound 2 (4-alkoxy-2,3-difluorobenzoic acid) was
obtained as colourless crystals in ca. 85% yield. Compound 2
was then esterified with 4-hydroxybenzaldehyde using
DCC–DMAP to give the aldehyde, 3, which was then con-
densed with various anilines. Crystallisation of the resulting
imines from dichloromethane–methanol, and then from tolu-
ene, gave the pure difluorinated imines, 4, which were reacted
smectic phase, could be reacted with [MMe(CO) ] (M=Mn,
5
Re) to give the orthometallated, tetracarbonyl derivative (e.g.
13) of the ligand which would clear at more than 100 °C lower
than the free ligand and would show only a nematic phase.
We were then able to show13c that by using shorter, three-ring
imines it was possible to realise materials with (monotropic)
clearing points as low as about 70 °C. We were therefore keen
to look at other strategies which might lead to lower melting
points and, therefore, we undertook a study of fluorinated
derivatives of the ligands and their metal complexes. Three,
four-ringed imines were chosen and both di- and tetra-fluori-
nated derivatives, and their complexes with rhenium, were
obtained.
with [ReMe(CO) ] in toluene at reflux. The resulting rhe-
nium() complexes (5) were purified by flash column chroma-
5
tography (neutral alumina), eluting with 20% hexanes–CH Cl
(v/v) to obtain the desired product in ca. 80% yield after
crystallisation from dichloromethane and hexanes.
2
2
The synthesis of the tetrafluoro-substituted rhenium
complexes, 9, (Scheme 2) required 4∞-(4-alkoxy-2,3-difluoro-
benzoyloxy)aniline derivatives in addition to the difluoro-
benzaldehydes 3. Thus, 4-alkoxy-2,3-difluorobenzoic acid was
esterified with 4-hydroxynitrobenzene using DCC–DMAP to
Results and Discussion
Synthesis
give the 4-alkoxy-2,3-difluorobenzoyloxy-4∞-nitrobenzene
6
Difluoroimines were synthesized in
a four-step reaction
which was then reduced to 4-alkoxy-2,3-difluorobenzoyloxy-
4∞-aniline derivatives using tin() chloride. The 4-alkoxy-2,3-
difluorobenzoyloxyaniline derivatives 7 were purified by flash
chromatography (silica gel), eluting with a solution of 1%
triethylamine in 10% MeOH–CH Cl (v5v5v). A brownish
(Scheme 1). The unsymmetrical ether 1 was first obtained in a
Williamson ether synthesis using 2,3-difluorophenol and the
related 1-bromoalkane in dimethylformamide. Lithiation was
then effected with an equimolar amount of butyllithium at
−78 °C, followed by quenching with solid carbon dioxide to
give a single product as detected by chromatographic (TLC)
analysis of the crude product mixture. The crude product was
2
2
product, 7, was obtained in ca. 70% yield, which was then
condensed with the difluorinated aldehyde derivatives 3 and
F
F
F
F
F
F
ii
i
CnH2n + 1
O
CnH2n + 1
O
CO2H
HO
2
1
iii
F
F
O
O
CnH2n + 1
O
+
CHO
H2N
O
O
OCmH2m + 1
3
iv
F
F
O
O
CnH2n + 1
O
N
O
4a
4b
4c
m
m
m
= 8,
= 8,
n
n
= 8
OCmH2m + 1
= 12
O
= 12,
n = 12
v
F
F
O
O
CnH2n + 1
O
CO N
Re
O
O
OCmH2m + 1
OC
5a
5b
5c
m
m
m
= 8,
= 8,
n
n
= 8
CO
= 12
CO
= 12,
n = 12
Scheme 1 Synthetic route to difluoro-substituted rhenium complexes 5. Reagents and conditions: i, C H
THF; iii, DCC, DMAP, DCM; iv, toluene–acetic acid; v, [ReMe(CO) ]–toluene.
Br, K CO , DMF; ii, BuLi, CO
,
n
2n+1
2
3
2(s)
5
1556
J. Mater. Chem., 1998, 8(7), 1555–1560

F
F
F
F
HO
O
i
O2N
O
O
OCmH2m + 1
OCmH2m + 1
6
2
ii
F
F
O
O
CnH2n + 1
O
F
F
+
CHO
H2N
O
O
OCmH2m + 1
3
7
iii
F
F
O
CnH2n + 1
O
O
F
F
N
O
O
8a m = 8, n = 8
8b m = 8, n = 12
8c m = 12, n = 12
OCmH2m + 1
iv
F
F
O
O
CnH2n + 1
O
F
F
CO N
O
O
OCmH2m + 1
Re
OC
9a m = 8, n = 8
9b m = 8, n = 12
9c m = 12, n = 12
CO
CO
Scheme 2 Synthetic route to tetrafluoro-substituted rhenium complexes 9. Reagents and conditions: i, DCC, DMAP, DCM, 4-nitrophenol;
ii, SnCl ·2H O, ethanol; iii, toluene–acetic acid; iv, [ReMe(CO) ]–toluene.
2
2
5
crystallised from CH Cl –hexanes and then toluene to give
compound 8 as colourless crystals. The tetrafluorinated imines
towards the end of the molecules, smectic phases are being
stabilised in the shorter chain compound, while nematic phases
are destabilised in the longer chain compounds. It is also of
interest that all of the more highly ordered smectic phases
have been suppressed. Further, if melting is taken to be the
formation of a fluid smectic phase, then melting points are
systematically lowered in the difluoro compounds and raised
in the tetrafluoro compounds. The former may be explained
by the unsymmetric nature of the imine, while the latter reflects
increased (and symmetric) intermolecular dipolar associations.
2
2
8 were reacted with [ReMe(CO) ] in toluene and the product
purified by flash column chromatography (neutral alumina),
5
eluting with 10% hexane–CH Cl (v/v) to give the desired
complexes 9 as yellow crystals in ca. 80% yield following
crystallisation from CH Cl –hexane.
2
2
2
2
Ligand mesomorphism
Table 1 shows the transition temperatures for the parent,
unsubstituted imine ligands 10, 11 and 12,14 and those of their
di- and tetra-fluorinated analogues, 4 and 8. Thus, 11 and 12
exhibit crystal J, smectic I, C and nematic phases, while 10
exhibits crystal G, smectic C and nematic phases. The meso-
morphism of these parent ligands and their fluorinated ana-
logues is collected in Fig. 4.
Mesomorphism of the complexes
The mesomorphism behaviour of the complexes is collected in
Table 2 along with the mesomorphism of the parent unfluori-
nated complexes; the behaviour is also illustrated graphically
in Fig. 6.
The mesomorphism of the di- and tetra-fluorinated deriva-
tives was rather similar in that all showed both a smectic C
and a nematic phase, with none of the more ordered smectic
phases being observed. The smectic C phase was characterised
by its schlieren texture and the observation of transition bars
on its transition to the nematic phase. The largest smectic C
ranges were consistently observed for the difluoro imines,
reaching nearly 150 °C in 4c, but this range was obtained by
a destabilisation of the crystal phase. The highest thermal
Reaction of the parent imines with [ReMe(CO) ] led to
complexes whose melting points (taken as the transition into
a fluid phase) increased by 20–30 °C and whose nematic phase
stability decreased by about 120 °C; all other phases were
suppressed. In the case of the fluorinated ligands, complexation
5
again led to the suppression of the S phase and the destabilis-
ation of the nematic phase. This destabilisation was quite
C
constant in the case of the tetrafluoro systems at 127 1 °C,
while it varied much more for the difluoro systems. In fact,
the drop in T on going from 4c to 5c is undetermined (except
stability for the S phase is with the tetrafluoro derivatives,
while the highest nematic phase stability was found in the
C
NI
that it is at least 118 °C) as the complex simply melted at
unsubstituted imines; the reduction in nematic range on
increased fluoro substitution is nicely illustrated in Fig. 5.
Clearly then, because of the position of the fluoro groups
141 °C with no sign of a monotropic phase before crystallisation
on cooling. Another interesting point is that the stabilisation
of the crystal phase on complexation shows a strong depen-
J. Mater. Chem., 1998, 8(7), 1555–1560
1557

Table 1 Thermal behaviour for the fluoro-substituted imines and their
parent compounds
X
X
O
O
CnH2n + 1
O
Y
Y
N
O
O
OCmH2m + 1
DH/kJ DS/JK−1
Compound
X
Y
n
m
transition
T/°C mol−1
mol−1
10
H
H
8
8
Crys–Crys’
Crys’–G
G–S
63
116
124
202
298
97
213
299
127
222
288
91
110
118
224
284
96
216
270
120
226
264
99
105
113
234
269
86
234
259
120
231
252
24.7
25.2
3.8
1.9
2.2
27.5
2.6
1.9
33.2
4.0
1.1
13.5
0.4
0.8
1.4
1.0
32.4
2.1
1.7
32.2
4.5
1.4
32.6
0.1
1.0
3.3
1.8
73
65
10
4
4
74
5
3
83
8
2
38
1
2
3
1
88
4
3
82
9
C
S –N
C
N–I
4a
8a
11
F
F
H
F
8
8
8
8
8
Crys–S
C
S –N
C
Fig. 5 Plot to show the decrease in the nematic range with increasing
fluorine substitution
N–I
Crys–S
C
S –N
C
Table 2 Thermal behaviour for the rhenium complexes of the fluoro-
substituted imines and their parent complexes
N–I
H
H
12
Crys–J
J–S
X
X
I
O
O
S –S
S –N
I
C
CnH2n + 1
O
Y
Y
C
N–I
Crys–S
CO
Re
N
O
O
4b
8b
12
F
F
H
F
12
12
8
OCmH2m + 1
C
C
OC
S –N
N–I
CO
C
CO
Crys–S
S –N
DH/
T/°C kJ mol−1
DS/J K−1
mol−1
C
Compound
X
Y
n
m
transition
N–I
12 12 Crys–J
3
H
H
88
>1
3
7
3
86
12
5
83
10
2
13
H
H
H
8
8
Crys–Crys’ 135
6.8
32.2
1.2
17.1
51.1
2.6
52.1
1.6
48.0
0.9
18.5
47.0
1
47.6
0.7
22.8
53.4
0.9
33.2
30.6
19.1
43.2
0.5
17
75
3
53
120
6
127
4
118
2
47
113
2
120
2
62
132
2
90
74
57
107
1
J–S
S –S
I
Crys’–N
N–I
Crys–Crys’
Crys’–N
N–I
Crys–N
N–I
Crys–N
N–I
154
176
48
153
164
137
160
130
164
I
C
S –N
N–I
C
5a
F
8
8
8
4c
8c
F
F
H
F
12 12 Crys–S
S –N
N–I
12 12 Crys–S
31.0
6.2
2.4
32.6
5.2
1.2
C
C
C
9a
14
5b
F
H
F
F
H
H
8
8
8
12
12
S –N
N–I
C
Crys–Crys’ 123
Crys’–N
N–I
Crys–N
N–I
143
149
125
138
96
9b
15
F
F
12
8
H
H
12 12 Crys–Crys’
Crys’–N
N–I
12 12 Crys–Crys’
Crys’–I
12 12 Crys–Crys’
Crys’–I
(N–I)
131
145
95
141
61
5c
9c
F
F
H
F
131
(125)
Fig. 4 Schematic representation of the mesomorphism of the non-
fluorinated, di- and tetra-fluorinated imines
dence on the degree of fluorination, with difluorinated systems
being stabilised by between 47 and 55 °C, while tetrafluorinated
systems are stabilised by only 5–11 °C. We have no simple
explanation for this phenomenon. However, the net effect is to
produce complexes with shorter mesomorphic ranges due to
destabilisation of the mesophase and stabilisation of the crystal
phase. This behaviour is true for all of the systems examined
and indeed, it would appear that the chain length has a larger
influence.
Fig. 6 Schematic representation of the mesomorphism in rhenium()
complexes of non-fluorinated, di- and tetra-fluorinated imines
These results are perhaps surprising given the more beneficial
1558
J. Mater. Chem., 1998, 8(7), 1555–1560

effects observed by Imrie and coworkers7 with fluorinated
ferrocenes, although it may just be that there is a more
advantageous fluorine substitution pattern in these imines
which will offer the chance of wider ranges and at lower
temperatures. This awaits further study.
ated under vacuum to give a yellow oil. Distillation under
vacuum at 69 °C (5×10−3 mm Hg) afforded a colourless oil.
CH ), 1.31–1.55 (m, 10H, 5CH ), 1.80 (m, 2H, OCH CH ),
Yield 92%, 1H NMR (200 MHz, CDCl ), d 0.90 (t, 3H,
3
3
2
2
2
4.03 (t, 2H, J=6.6 Hz, OCH ), 6.75 (m, 2H, aromatic) and
2
6.97 (m, 1H, aromatic). MS: m/z 242 (M+).
Experimental
2,3-Difluoro-4-octyloxybenzoic acid 2. A solution of the 2,3-
difluoro-4-octyloxybenzene 1 (3.0 g, 12.4 mmol) in dry THF
(100 cm3) was blanketed with nitrogen and then treated drop-
wise at −78 °C with butyllithium in hexane (7.75 cm3 in 1.6 
hexanes). When the addition was complete, the mixture was
stirred for ca. 5 h at the same temperature and then poured
into ca. 100 g of crushed, solid carbon dioxide. After 15 h the
residue was treated with 10% aqueous sodium bicarbonate
and then with diethyl ether. The aqueous layer was separated,
washed with diethyl ether, acidified with cold concentrated
hydrochloric acid, and extracted with chloroform. The com-
bined chloroform extracts were dried over anhydrous Na SO ,
Characterisation
Microanalyses were performed at Department of Chemistry,
University of Exeter and Quantitative Technologies Inc.,
Whitehouse, NJ, Micro-analytical Service. Mass spectra were
obtained with the use of a VG 70-250S mass spectrometer
operating in electron impact (EI) mode. All chemicals were
used as received unless otherwise specified. IR spectra were
recorded on a Nicolet Magna 550 IR spectrometer at
University of Toronto. Spectra were recorded as Nujol mulls
between polythene plates, or as CH Cl solutions, or KBr
disks. 1H NMR spectra were recored on a Varian Gemini 200
spectrometer; chemical shifts are quoted relative to an internal
duterium lock. 19F NMR spectra were recorded on a Varian
Gemini 300 spectrometer and CFCl was used as reference.
The melting points and phase transitions of liquid crystal
materials were observed by differential scanning calorimetry
(DSC) using a Perkin-Elmer DSC7 system with a Perkin-
Elmer 7000 data station using TAS 7 software. Visual charac-
terisation of the liquid-crystalline properties of the bulk mate-
rials was performed using a polarising optical microscope
equipped with a Mettler FP82 hot stage and FP80 central
processor at University of Toronto.
Toluene and tetrahydrofuran were distilled over sodium/
benzophenone under nitrogen immediately before use.
Dichloromethane was dried over molecular sieves (4A) for at
least 24 h before use. All other solvents were used as received
without further purification.
2
2
2
4
and TLC analysis of the extract showed the presence of one
significant product. The solvent was removed in vacuo to give
a white residue, which was purified by crystallisation from
chloroform.
3
Yield, 2.99 g (84.6%), 1H NMR (200 MHz, CDCl ), d 0.90
(t, 3H, CH ), 1.25–1.65 (m, 10H, 5CH ), 1.86 (m, 2H,
3
3
2
OCH CH ), 4.09 (t, 2H, OCH ), 6.8 (m, 1H, aromatic) and 7.8
(m, 1H, aromatic), 9.0 (br s, CO H). 19F NMR (300 MHz,
2
2
2
2
CD Cl ), d −132.93 (dd), −158.65 (dd). MS: m/z 286 (M+)
2
2
(HRMS: found: M+, 286.1381. C H F O requires 286.1368).
15 20 2
3
4∞-(4-Alkoxy-2,3-difluorobenzoyloxy)benzaldehyde 3. All
esters were obtained using this general procedure.
Dicyclohexyl carbodiimide (5.94 g, 28.8 mmol) and 4-(N,N-
dimethylamino)pyridine (0.15 g) were added to a stirred solu-
tion of the relevant acid (24 mmol) and hydroxybenzaldehyde
(3.0 g, 24.0 mmol) in dry dichloromethane (100 cm3). The
reaction mixture was stirred at room temperature for 6 h. The
precipitated dicyclohexyl urea was removed by filtration and
the residue was reduced to dryness on a rotary evaporator.
The crude product was purified by column chromatography
(silica gel, CH Cl ) to give the product as a colourless solid.
Synthesis
In all cases, the synthesis for one example is given along with
the relevant spectroscopic data. All other homologues were
the same with analogous spectra. Analytical data and yields
are collected in Table 3.
2
2
n=8; yield: 67.3%, 1H NMR (200 MHz, CDCl ), d 0.90 (t,
3H, CH ), 1.25–1.65 (m, 10H, 5CH ), 1.86 (m, 2H, OCH CH ),
3
3
2
2
2
4.09 (t, 2H, OCH ), 6.8 (m, 1H, aromatic), 7.45 (d, 2H, AA∞XX∞),
7.87 (dd, 1H, aromatic), 8.0 (dd, 2H, AA∞XX∞), 10.0 (s, 1H,
2,3-Difluoro-4-octyloxybenzene 1. A mixture of 4-hydroxy-
2,3-difluorobenzene (5.0 g, 38.4 mmol), 1-bromooctane (8.9 g,
46.1 mmol) and potassium carbonate (14.0 g, 96 mmol) in
DMF (130 cm3) was refluxed for 6 h. After cooling to room
temperature, water (100 cm3) was added in the flask to dissolve
salt and then the product was extracted with diethyl ether
three times. The extracts were washed with water and then
2
CHO). 19F NMR (300 MHz, CD Cl ), d −132.14 (dd),
2
2
−157,64 (dd). MS: m/z 391 (MH+), 269, 157(100%) (HRMS:
found: MH+, 391.1721. C H F O requires M, 391.1711).
22 24 2
4
4∞-(4-Alkyloxy-2,3-difluorobenzoyloxy)nitrobenzene 6. For
the compounds 6, the synthesis was performed in an analogous
manner as 3 above.
dried over CaCl overnight. After filtration, ether was evapor-
2
m=8; yield: 74.2%, 1H NMR (200 MHz, CDCl ), d 0.90 (t,
3H, CH ), 1.25–1.65 (m, 10H, 5CH ), 1.86 (m, 2H, OCH CH ),
Table 3 Analytical data for the ligands and complexes
3
3
2
2
2
calc. (found)
4.15 (t, 2H, OCH ), 6.86 (dd, 1H, aromatic), 7.43 (d, 2H,
AA∞XX∞), 7.87 (dd, 1H, aromatic), 8.34 (dd, 2H, AA∞XX∞).
2
compound
yield (%)
C
H
N
4∞-(4-Alkyloxy-2,3-difluorobenzoyloxy)aniline 7. All anilines
were obtained from the parent nitro compound according to
the following general method.
ligands
4a
4b
83
75
78
83
81
76
72.0 (72.4)
73.3 (73.2)
74.1 (73.8)
68.9 (68.7)
70.0 (70.1)
71.1 (70.9)
6.9 (6.9)
7.5 (7.3)
7.9 (7.8)
6.3 (6.2)
7.0 (7.3)
7.4 (7.2)
1.9 (2.0)
1.8 (1.8)
1.7 (1.7)
1.9 (1.8)
1.9 (1.8)
1.6 (1.6)
4c
8a
A mixture of the nitrobenzene (13 mmol) and SnCl ·2H O
2
2
(15.2 g, 65 mmol) was heated at reflux in ethanol (100 cm3) for
6 h. After cooling, the mixture was poured into ice and the pH
was adjusted to ca. 7–8 using sodium hydroxide. The mixture
was then extracted with ethyl acetate. The ethyl acetate solu-
tion was washed three times with brine and was then dried
8b
8c
complexes
5a
5b
5c
9a
9b
9c
77
82
78
83
72
75
55.8 (55.6)
57.4 (57.1)
58.8 (58.5)
53.9 (53.6)
55.5 (55.2)
57.0 (56.6)
4.8 (4.9)
5.3 (5.1)
5.7 (5.6)
4.4 (4.3)
4.9 (5.1)
5.4 (5.3)
1.4 (1.4)
1.3 (1.3)
1.3 (1.2)
1.3 (1.3)
1.3 (1.3)
1.2 (1.2)
over anhydrous MgSO . The solvent was evaporated under
reduced pressure. The brownish solid was purified by column
4
chromatography (silica gel: 1% Net –CH Cl , v/v) and then
crystallised from ethanol to give an off-white solid.
3
2 2
J. Mater. Chem., 1998, 8(7), 1555–1560
1559

n=8; yield: 71%, 1H NMR (200 MHz, CDCl ), d 0.90 (t,
3H, CH ), 1.25–1.65 (m, 10H, 5CH ), 1.86 (m, 2H, OCH CH ),
8.5 (s, 1H, CHNN). 19F NMR (300 MHz, CD Cl ), d −132.30
3
2 2
(dd, 1F, J=19.6, 7.9 Hz), −132.47 (dd, 1F, J=19.7, 7.1 Hz),
−157.73 (dd, 1F, J=18.7, 8.1 Hz), −157.85 (dd, 1F, J=
19.3, 8.5 Hz).
3
2
2
2
3.35 (br s, 2H, NH ), 4.1 (t, 2H, OCH ), 6.7 (dd, 2H, AA∞XX∞),
6.8 (dd, 1H, aromatic), 7.0 (dd, 2H, AA’XX’), 7.82 (dd, 1H,
2
2
aromatic). 19F NMR (300 MHz, CD Cl ), d −132.77 (dd),
2
2
−158.03 (dd). MS: m/z 377 (M+), 269, 157 (100%), 108, 57
377.1809).
Tetrafluoro-substituted rhenium(I ) complexes 9. Tetrafluoro-
substituted rhenium() complexes 9 were obtained in a manner
analogous to that used in complexes 5.
(HRMS: found: M+, 377.1803. C H F O requires M,
21 25 2
3
9a: IR (CH Cl solution) n /cm−1: 2093w (CO), 1992vs
2
2
max
(CO), 1934m (CO) and 1735m (CNO), 1623w (CNN). 1H
NMR (200 MHz, CD Cl ), d 0.9 (t, 6H, 2CH overlapped),
1.25–1.65 (m, 20H, 10CH ), 1.86 (m, 4H, 2OCH CH ), 4.15 (t,
Difluoro-substituted imines 4. All imines were obtained using
the following general procedure.
2
2
2
3,
2
The relevant aniline (19.2 mmol) was dissolved in toluene
(25 cm3) and then acetic acid (2 drops) was added to the
solution. The relevant aldehyde (19.2 mmol) was added to the
solution which was stirred for a few minutes then left unstirred
overnight. The crude product was filtered and crystallised from
CH Cl –MeOH and then from toluene, to give a colourless,
2
4H, J=6.6 Hz, OCH ), 6.9 (ddd, 2H, aromatic, overlapped),
2
7.08 (dd, 1H, J=8.2 Hz, 2.4), 7.36 (m, 4H, AA∞XX∞), 7.8–7.93
(m, 4H, 2AMX+2aromatic), 8.65 (s, 1H, CHNN). 19F NMR
(300 MHz, CD Cl ), d −132.26 (dd, 1F, J=19.3, 8.1 Hz),
2
2
−132.44 (dd, 1F, J=19.3, 8.1 Hz), −157.72 (dd, 1F, J=19.2,
6.6 Hz), −157.83 (dd, 1F, J=19.3, 7.1 Hz).
2
2
crystalline product.
4a: 1H NMR (200 MHz, CDCl ), d 0.88 (t, 6H, 2CH ),
1.25–1.65 (m, 20H, 10CH ), 1.86 (m, 4H, 2OCH CH ), 4.05 (t,
3
3
We thank the University of Sheffield and NSERC for funding.
2
2
2
2H, J=6.6 Hz, OCH ), 4.14 (t, 2H, J=6.5 Hz, OCH ), 6.81
2
2
(ddd, 1H, aromatic), 7.0 (dd, 2H, AA∞XX∞), 7.2–7.4 (m, 6H,
AA∞XX∞), 7.82 (ddd, 1H, aromatic), 8.0 (d, 2H, AA∞XX∞), 8.17
(d, 2H, AA∞XX∞), 8.5 (s, 1H, CHNN). 19F NMR (300 MHz,
CD Cl ), d −132.30 (dd, 1F, J=19.7, 8.2 Hz), −157.74 (dd,
References
1
2
3
V. Vill, L iqCryst 3.0, LCI Publishers, Hamburg.
L. D. Field and S. Sternhell, J. Am. Chem. Soc., 1981, 103, 738.
(a) M. A. Osman, Mol. Cryst. L iq. Cryst., 1985, 128, 45; (b)
G. W. Gray, in Molecular Structure and the Properties of L iquid
Crystals, Academic Press, London, 1962; (c) G. W. Gray, in L iquid
Crystals and Plastic Crystals, ed. G. W. Gray and P. A. Winsor,
Ellis Horwood Limited, Chichester, 1974, vol. 4; (d) K. J. Toyne, in
T hermotropic L iquid Crystals, ed. G. W. Gray, Wiley, Chichester,
1987, pp. 28–63.
(a) S. M. Kelly, Helv. Chim. Acta, 1989, 72, 594; (b) A. J. Seed,
K. J. Toyne and J. W. Goodby, J. Mater. Chem., 1995, 5, 2201.
G. W. Gray, M. Hird and K. J. Toyne, Mol. Cryst., L iq. Cryst.,
1991, 204, 43.
D. W. Bruce and S. A. Hudson, J. Mater. Chem., 1994, 4, 479.
C. Loubser, C. Imrie and P. H. v. Rooyen, Adv. Mater., 1993, 5, 45.
E. Bui, J. P. Bayle, F. Perez, L. Liebert and J. Courtieu, L iq. Cryst.,
1991, 8, 5213.
A. B. Blake, J. R. Chipperfield, W. Hussain, R. Paschke and
E. Sinn, Inorg. Chem., 1995, 34, 1125.
2
2
1F, J=18.7, 8.1 Hz).
Difluoro-substituted rhenium(I ) complexes 5. All difluoro-
substituted rhenium() complexes 5 were synthesised in an
analogous manner using the following method.
Ligand 4a (0.15 g, 0.21 mmol) and (pentacarbonylmethyl)-
rhenium (0.07 g, 0.21 mmol) were dissolved in dry toluene and
heated at reflux for 12–16 h under nitrogen. Solvent was then
removed in vacuo and passed through a column of neutral
alumina eluting with hexanes–CH Cl (1:4, v/v) to obtain the
4
5
6
7
8
2
2
desired rhenium() complex fraction. Following crystallisation
from CH Cl –MeOH, yellow crystalline product was
obtained.
a
2
2
9
5a; yield 76.7%, IR (CH Cl solution) n/cm−1: 2093w (CO),
2
2
1992vs (CO), 1987s (CO), 1934m (CO) and 1731(CNO), 1606
(CNN). 1H NMR (200 MHz, CD Cl ), d 0.88 (t, 6H, 2CH ),
1.25–1.65 (m, 20H, 10CH ), 1.86 (m, 4H, 2OCH CH ), 4.05 (t,
10 D. W. Bruce, R. Dhillon, D. A. Dunmur and P. M. Maitlis,
J. Mater. Chem., 1992, 2, 65.
11 N. J. Thompson, G. W. Gray, J. W. Goodby and K. J. Toyne, Mol.
Cryst., L iq. Cryst., 1991, 200, 109.
12 D. W. Bruce, Adv. Mater., 1994, 6, 699; J. P. Rourke, D. W. Bruce
and T. B. Marder, J. Chem. Soc., Dalton T rans., 1995, 317;
S. Morrone, G. Harrison and D. W. Bruce, Adv. Mater., 1995, 7,
665; K. E. Rowe and D. W. Bruce, J. Chem. Soc., Dalton T rans.,
1996, 3913; S. Morrone, D. Guillon and D. W. Bruce, Inorg. Chem.,
1996, 35, 7041.
2
2
3
2
2
2
2H, J=6.6 Hz, OCH ), 4.14 (t, 2H, J=6.5 Hz, OCH ), 6.9
2
2
(ddd, 1H, aromatic), 7.05 (m, 3H), 7.4 (m, 4H, AA∞XX∞), 7.82
(dd, 2H), 7.9 (d, 1H, aromatic), 8.15 (d, 2H, AA∞XX∞), 8.67 (s,
1H, CHNN). 19F NMR (300 MHz, CD Cl ), d −132.43 (dd,
2
2
1F, J=19.3, 7.8 Hz), −157.82 (dd, 1F, J=19.2, 6.6 Hz).
13 (a) D. W. Bruce and X.-H. Liu, J. Chem. Soc., Chem. Commun.,
1994, 729; (b) D. W. Bruce and X.-H. Liu, L iq. Cryst., 1995, 18, 165;
(c) X.-H. Liu, M. N. Abser and D. W. Bruce, J. Organomet. Chem.,
1998, 551, 271.
Tetrafluoro substituted imine ligands 8. The imine ligands 8
were obtained in an analogous manner as those of ligands 4.
8a: 1H NMR (200 MHz, CDCl ), d 0.88 (t, 6H, 2CH ),
3
3
1.25–1.65 (m, 20H, 10CH ), 1.86 (m, 4H, 2OCH CH ), 4.15 (t,
14 X.-H. Liu, PhD Thesis, University of Sheffield, 1997.
2
2
2
4H, J=6.5 Hz, 2OCH ), 6.81 (ddd, 2H, aromatic), 7.2–7.4 (m,
2
6H, AA∞XX∞), 7.87 (ddd, 2H, aromatic), 8.0 (d, 2H, AA∞XX∞),
Paper 8/02167H; Received 19th March, 1998
1560
J. Mater. Chem., 1998, 8(7), 1555–1560