DE4000534C2 - 1,4-disubstituted 2,6-difluorobenzene compounds and liquid-crystalline medium - Google Patents

Description

The invention relates to new 1,4-disubstituted 2,6-difluorobenzene compounds of the formula I,

wherein
R ¹ H or an unsubstituted or one at least monosubstituted by halogen or alkyl or alkenyl radical having 1 to 15 carbon atoms, one or more CH ₂ groups in each of these radicals also being carried out independently of one another

can be replaced in such a way that O atoms are not directly linked to one another,
R ^{2 is} an alkyl or alkenyl radical having 1 to 15 carbon atoms which is at least monosubstituted by halogen, and one or more CH ₂ groups in these radicals are each independently of one another

can be replaced in such a way that O atoms are not directly linked to one another,
A ¹ and A ² each independently have one

• a) trans-1,4-cyclohexylene radical, in which one or more non-adjacent CH ₂ groups can also be replaced by -O- and / or -S-,
• b) 1,4-phenylene radical, in which one or two CH groups can also be replaced by N,
• c) remainder from the group 1,4-cyclohexenylene, 1,4-bicyclo (2,2,2) -octylene, piperidine-1,4-diyl, naphthalene-2,6-di yl, decahydronaphthalene-2,6-diyl and 1,2,3,4-tetrahydronaphthalene-2,6-diyl,

where the radicals (a) and (b) can be substituted by CN or fluorine,
No. ¹

and Z ²

each independently of one another -CO-O-, -O-CO-, -CH ₂

O-, -OCH ₂

-, -CH ₂

CH ₂

-, -CH = CH-, -C∼C- or a single bond,
m and n each independently of one another 0, 1 or 2, where
(m + n) is 1, 2 or 3,
with the proviso that at least one of the im
^{Residues A 1} present in the molecule

and A ²

means.

The invention further relates to the use of these compounds as components of liquid crystalline Media, as well as liquid crystal and electro-optical display elements, the liquid crystal according to the invention Media included.

The compounds of the formula I can be used as components of liquid-crystalline media, especially for displays based on the principle of the twisted cell, the guest-host effect, the effect of the Deformation of erect phases or the effect of dynamic scattering.

The invention was based on the object of providing new stable liquid-crystalline or mesogenic compounds find which are suitable as components of liquid-crystalline media and in particular at the same time a ver have a comparatively low viscosity and a relatively high dielectric anisotropy.

It has now been found that compounds of the formula I are preferred as components of liquid-crystalline media are suitable. In particular, they have comparatively low viscosities. With their help you can liquid-crystalline media with a broad mesophase range and advantageous values for the optical and dielectric properties tric anisotropy with excellent UV and temperature stability.

Liquid crystals of the formula

are already known from WO 89/02 425 and are characterized by high and relatively high birefringence Viscosity off.

From DE 32 09 178 A1 polyhalogenoaromatics and their use as components of liquid-crystalline dielectrics are known, these polyhalogenoaromatics having no halogenated radical R ² and no second fluorinated phenylene ring A ¹ or A ² . The 4,4'-bis (cyclohexyl) biphenyl derivatives known from DE 31 17 152 A1, which can also be used as components of liquid-crystalline dielectrics, do not have a halogenated radical R ² .

With regard to the most diverse areas of application of such compounds with positive Δε it was it is desirable to have further connections available that are specific to the respective applications have tailor-made properties.

With the provision of compounds of the formula I, the range of liquid-crystalline substances which, from various application points of view, can be used to produce position liquid-crystalline mixtures are suitable, considerably broadened.

The compounds of the formula I have a wide range of applications. Depending on the selection of the substituents, these compounds can serve as base materials from which liquid-crystalline media are predominantly composed; however, compounds of the formula I can also be liquid-crystal linen base materials from other classes of compounds can be added, for example dielectric and / or to influence the optical anisotropy of such a dielectric and / or to its threshold span tion and / or to optimize its viscosity.

The compounds of the formula I are colorless in the pure state and form liquid-crystalline mesophases in a temperature range that is conveniently located for electro-optical use. Chemically, thermally and they are stable to light.

The invention thus relates to the compounds of the formula I.

The invention also relates to liquid-crystalline ones Media containing at least one compound of the formula I and liquid crystal display elements, in particular electro-optical display elements that contain such media.

For the sake of simplicity, A ³ in the following denotes a radical of the formula

Cyc is a 1,4-cyclohexylene radical,
A ^{4 is} a radical of the formula

Che a 1,4-cyclohexenylene radical, Dio a 1,3-dioxane-2,5-diyl radical, Dit a 1,3-dithiane-2,5-diyl radical, Phe a 1,4-phenylene radical, Pyd a pyridine-2,5-diyl radical, Pyr a pyrimidine-2,5-diyl radical and Bi a bicyclo (2,2,2) -octy lenrest.

The compounds of the formula I accordingly include the preferred compounds with two rings of the sub-formulas Ia and Ib:

R ¹ -A ³ -A ² -R ² (Ia)

R ¹ -A ³ -Z ² -A ² -R ² (Ib)

Compounds with three rings of the sub-formulas Ic to If:

R ¹ -A ³ -Z ² -A ² -Z ² -A ² -R ² (Ic)

R ¹ -A ¹ -Z ¹ -A ³ -Z ² -A ² -R ² (Id)

R ¹ -A ¹ -Z ¹ -A ⁴ -Z ¹ -A ³ -R ² (Ie)

R ¹ -A ⁴ -Z ¹ -A ¹ -Z ¹ -A ³ -R ² (If)

as well as compounds with four rings of the sub-formulas Ig to Ij:

R ¹ -A ¹ -Z ¹ -A ³ -Z ² -A ² -Z ² -A ² -R ² (Ig)

R ¹ -A ¹ -Z ¹ -A ¹ -Z ¹ -A ³ -Z ² -A ² -R ² (Ih)

R ¹ -A ¹ -Z ¹ -A ¹ -Z ¹ -A ⁴ -Z ¹ -A ³ -R ² (Ii)

R ¹ -A ¹ -Z ¹ -A ⁴ -Z ¹ -A ¹ -Z ¹ -A ³ -R ² (Ij)

Of these, those of the sub-formulas Id, Ie, Ih and Ii are particularly preferred.

Some particularly preferred, smaller groups of compounds are given below:

In the compounds of the formulas ^{above and below, R 1 is} preferably alkyl or alkoxy. A ¹ and / or A ^{2 are} preferably Phe, Cyc, Che, Pyr or Dio. The compounds of the formula I preferably contain no more than one of the radicals Bi, Pyd, Pyr, Dio or Dit.

Compounds of the formula I and all sub-formulas in which A ¹ and / or A ^{2 is} 1,4-phenylene which is monosubstituted or disubstituted by F are also preferred. In particular, these are 2-fluoro-1,4-phenylene, 3-fluoro-1,4-phenylene and 2,3-difluoro-1,4-phenylene.

Z ¹ and Z ² preferably denote a single bond, -CO-O-, -O-CO- and -CH ₂ CH ₂ -, in the second place preferably -CH ₂ O- and -OCH ₂ -. Preferably only one of the groups Z ¹ and Z ² present in the molecule is different from the single bond.

If R ¹ or R ^{2 is} an alkyl radical and / or an alkoxy radical, this can be straight-chain or branched. It is preferably straight-chain, has 2, 3, 4, 5, 6 or 7 carbon atoms and is therefore preferably ethyl, propyl, butyl, pentyl, hexyl, heptyl, ethoxy, propoxy, butoxy, pentoxy, hexoxy or heptoxy, and also methyl , Octyl, nonyl, decyl, undecyl, dodecyl, tridecyl, tetradecyl, pentadecyl, methoxy, octoxy, nonoxy, decoxy, undecoxy, dodecoxy, tridecoxy or tetradecoxy, where the radical R ^{2 is} at least once substituted by halogen.

Oxaalkyl is preferably straight-chain 2-oxapropyl (= methoxymethyl), 2- (= ethoxymethyl) or 3-oxabutyl (= 2-methoxyethyl), 2-, 3- or 4-oxapentyl, 2-, 3-, 4- or 5-oxahexyl, 2-, 3-, 4-, 5- or 6-oxaheptyl, 2-, 3-, 4-, 5-, 6- or 7-oxaoctyl, 2-, 3-, 4-, 5-, 6-, 7- or 8-oxanonyl, 2-, 3-, 4-, 5-, 6-, 7-, 8- or 9-oxadecyl.

If R ¹ or R ² denotes an alkyl radical in which one CH ₂ group has been replaced by —CH =CH—, this can be straight-chain or branched. It is preferably straight-chain and has 2 to 10 carbon atoms. Accordingly, it means in particular vinyl, prop-1- or prop-2-enyl, but-1-, 2- or but-3-enyl, pent-1-, 2-, 3- or pent-4-enyl, hex -1-, 2-, 3-, 4- or hex-5-enyl, hept-1-, 2-, 3-, 4-, 5- or hept-6-enyl, oct-1-, 2-, 3-, 4-, 5-, 6- or oct-7-enyl, non-1, 2-, 3-, 4-, 5-, 6-, 7- or non-8-enyl, dec-1- , 2-, 3-, 4-, 5-, 6-, 7-, 8- or dec-9-enyl, where the radical R ^{2 is} at least once substituted by halogen.

If R ¹ or R ² denotes an alkyl radical in which one CH ₂ group has been replaced by -O- and one has been replaced by -CO-, these are preferably adjacent. Thus they contain an acyloxy group -CO-O- or an oxycarbonyl group -O-CO-. These are preferably straight-chain and have 2 to 6 carbon atoms.

Accordingly, they mean especially acetyloxy, propionyloxy, butyryloxy, pentanoyloxy, hexanoyloxy, acetyloxymethyl, propionyloxymethyl, butyryloxymethyl, pentanoyloxymethyl, 2-acetyloxyethyl, 2-propionyloxyethyl, 2-propionyloxyethyl, 2-butyryloxybutyl, 2-butyryloxybutyl, propyloxy, 3-propyloxybutyl, propyloxy, 3-propyloxybutyl, propyloxy, 3-butyryloxybutyl, propionyloxypropyl, hexanoyloxy, propyryloxy-ethyl Ethoxycarbonyl, propoxycarbonyl, butoxycarbonyl, pentoxycarbonyl, methoxycarbonylmethyl, ethoxycarbonylmethyl, propoxycarbonylmethyl, butoxycarbonylmethyl, 2- (methoxycarbonyl) ethyl, 2- (ethoxycarbonyl) ethyl, 2- (propoxycarbonyl) ethyl, 3- (methoxycarbonyl) propyl, 3- ( Ethoxycarbonyl) propyl, 4- (methoxycarbonyl) butyl, where the radical R ^{2 is} at least once substituted by halogen.

If R ¹ or R ^{2 is} an alkyl radical in which one CH ₂ group has been replaced by unsubstituted or substituted -CH = CH- and an adjacent CH ₂ group has been replaced by CO or CO-O or O-CO-, then this be straight-chain or branched. It is preferably straight-chain and has 4 to 13 carbon atoms. Accordingly, it means in particular acryloyloxymethyl, 2-acryloyloxyethyl, 3-acryloyloxypropyl, 4-acryloyloxybutyl, 5-acryloyloxypentyl, 6-acryloyloxyhexyl, 7-acryloyloxyheptyl, 8-acryloyloxyoctyl, 8-acryloyloxyoctyl, 3-acryloyloxyethyl, 3-acryloyloxyoctyl, 3-acryloyloxyethyl, 3-acryloyloxyoctyl, 3-acryloyloxyoctyl, 3-acryloxyethyl, 2-acryloyloxyoctyl, 3-acryloyloxyacryethyl, 4-acryloyloxybutyl, 4-acryloyloxybutyl. Methacryloyloxypropyl, 4-methacryloyloxybutyl, 5-methacryloyloxypentyl, 6-methacryloyloxyhexyl, 7-methacryloyloxyheptyl, 8-methacryloyloxy octyl, 9-methacryloyloxynonyl, where the radical R ^{2 is} at least once substituted by halogen.

Compounds of the formula I which have wing groups R which are suitable for polymerization reactions, are suitable for the preparation of liquid crystalline polymers.

Compounds of the formula I with branched wing groups R ¹ or R ² can occasionally be of importance because of better solubility in the customary liquid-crystalline base materials, but in particular as chiral dopants if they are optically active. Smectic compounds of this type are suitable as components for ferroelectric materials.

Compounds of the formula I with S _A phases are suitable, for example, for thermally addressed displays.

Branched groups of this type usually contain no more than one chain branch. Preferred branched radicals R are isopropyl, 2-butyl (= 1-methylpropyl), isobutyl (= 2-methylpropyl), 2-methylbutyl, Isopentyl (= 3-methylbutyl), 2-methylpentyl, 3-methylpentyl, 2-ethylhexyl, 2-propylpentyl, isopropoxy, 2-Me ethylpropoxy, 2-methylbutoxy, 3-methylbutoxy, 2-methylpentoxy, 3-methylpentoxy, 2-ethylhexoxy, 1-methylhe xoxy, 1-methylheptoxy.

If R ¹ or R ^{2 represents} an alkyl radical in which two or more CH ₂ groups have been replaced by —O— and / or —CO — O—, this can be straight-chain or branched. It is preferably branched and has 3 to 12 carbon atoms. It therefore means especially bis-carboxy-methyl, 2,2-bis-carboxy-ethyl, 3,3-bis-carboxy-propyl, 4,4-bis-carboxy-butyl, 5,5-bis-carboxy-pentyl, 6,6-bis-carboxyhexyl, 7,7-bis-carboxy-heptyl, 8,8-bis-carboxy-octyl, 9,9-bis-carboxy-nonyl, 10,10-bis-carboxy-decyl, bis - (methoxycarbonyl) methyl, 2,2-bis (methoxycarbonyl) ethyl, 3,3-bis (methoxycarbonyl) propyl, 4,4-bis (methoxycarbonyl) butyl, 5,5-bis (methoxycarbonyl) pentyl, 6,6-bis (methoxycarbonyl) hexyl, 7,7-bis (methoxycarbonyl) heptyl, 8,8-bis (methoxycarbonyl) -oc tyl, bis (ethoxycarbonyl) - methyl, 2,2-bis (ethoxycarbonyl) ethyl, 3,3-bis (ethoxycarbonyl) propyl, 4,4-bis (ethoxycarbonyl) butyl, 5,5-bis (ethoxycarbonyl) hexyl , where the radical R ^{2 is} at least once substituted by halogen.

Compounds of the formula I which have wing groups R ¹ or R ² suitable for polycondensations are suitable for the preparation of liquid-crystalline polycondensates.

Formula I includes both the racemates of these compounds and the optical antipodes as well as their Mixtures.

Of these compounds of the formula I and the sub-formulas, those in which at least one of the radicals contained therein has one of the preferred meanings given.

In the compounds of the formula I, those stereoisomers are preferred in which the rings Cyc and Piperidines are trans-1,4-disubstituted. Those of the above formulas that contain one or more Containing groups Pyd, Pyr and / or Dio, each enclose the two 2,5-position isomers.

The 1,4-cyclohexenylene group preferably has the following structures:

The compounds of the formula I are prepared according to methods known per se, as they are in the literature (e.g. in standard works such as Houben-Weyl, Methods of Organic Chemistry, Georg-Thieme-Verlag, Stuttgart Vol. IX, pp. 867 ff.) Are described, under reaction conditions which are for the mentioned Implementations are known and suitable. One can also use things that are known per se, but not here make use of the variants mentioned.

The compounds of the invention can, for. B. prepared by adding a compound of formula II,

in which R ¹ , A ¹ , Z ¹ and m have the meaning given, reacts according to the following reaction schemes:

Further synthetic methods are obvious to the person skilled in the art. For example, 1,3-difluorobenzene compounds correspondingly substituted in the 5-position can be converted into the 2-substituted 1,3-difluoro compounds according to the above scheme and the radical R ¹ - (A ¹ -Z ¹ ) _m - then through in the liquid Reactions customary in stable chemistry (e.g. esterification, etherification or couplings e.g. according to the article E. Poetsch, Kontakt (Darmstadt) 1988 (2), p. 15) can be introduced or vice versa.

The compounds of the formula II can be prepared, for example, according to the following synthesis schemes:

Scheme 1

Scheme 2

Scheme 3

Scheme 4

Scheme 5

The starting materials are either known or can be prepared in analogy to known compounds getting produced.

Esters of the formula I can also be prepared by esterification of corresponding carboxylic acids (or their reactive gen derivatives) with alcohols or phenols (or their reactive derivatives) or according to the DCC method de (DCC = dicyclohexylcarbodiimide).

The corresponding carboxylic acids and alcohols or phenols are known or can be prepared in analogy to known processes or by reacting metalated II with suitable electrophiles (B (OH) ₃ / H ₂ O ₂ or CO ₂ ).

The synthesis of some particularly preferred compounds is given below (Y = H or F):

Scheme 6 (Y = H or F)

In a further process for the preparation of the compounds of the formula I, an aryl halide is added an olefin in the presence of a tertiary amine and a palladium catalyst (cf. R. F. Heck, Acc. Chem. Res. 12 (1979) 146). Suitable aryl halides are, for example, chlorides, bromides and iodides, esp special bromides and iodides. The tertiary amines required for the coupling reaction to succeed, such as z. B. triethylamine, are also suitable as solvents. As palladium catalysts, for example, are Salts, especially Pd (II) acetate, with organic phosphorus (III) compounds such. B. triarylphosphines suitable. You can do this in the presence or absence of an inert solvent at temperatures operate between about 0 ° and 150 °, preferably between 20 ° and 100 °; as solvents come z. B. Nitriles such as acetonitrile or hydrocarbons such as benzene or toluene are suitable. As starting materials The aryl halides and olefins used are in many cases commercially available or can be found in the literature th process can be produced, for example by halogenation of appropriate parent compounds or by elimination reactions on corresponding alcohols or halides.

In this way, for example, stilbene derivatives can be produced. The stilbenes can still be manufactured are achieved by reacting a 4-substituted benzaldehyde with a corresponding phosphorylide Wittig. But you can also prepare tolanes of the formula I by monosubstituted instead of the olefin Acetylene is used (Synthesis 627 (1980) or Tetrahedron Lett. 27, 1171 (1986)).

Furthermore, aryl halides can be reacted with aryl zinc compounds for coupling aromatics the. These reactions are preferred with the addition of a catalyst such. B. a palladium (0) complex in inert solvents such as hydrocarbons at high temperatures, e.g. B. in boiling xylene, under Protective gas carried out.

Couplings of alkynyl compounds with aryl halides can be carried out analogously to that of A. O. King, E. Negishi, F. J. Villani and A. Silveira in J. Org. Chem. 43, 358 (1978).

Tolanes of the formula I can also be obtained via the Fritsch-Buttenberg-Wiechell rearrangement (Ann. 279, 319, 332, 1984) be prepared in the 1,1-diaryl-2-halogenethylenes are rearranged to diarylacetylenes in the presence strong bases.

Tolans of the formula I can also be prepared by brominating the corresponding stilbenes and then subjected to dehydrohalogenation. One can be familiar with it, but not here apply the mentioned variants of this implementation.

Ethers of the formula I are obtainable by etherification of corresponding hydroxy compounds, preferably corresponding phenols, the hydroxy compound expediently first being converted into a corresponding metal derivative, eg. B. by treatment with NaH, NaNH ₂ , NaOH, KOH, Na ₂ CO ₃ or K ₂ CO _{3 is converted} into the corresponding alkali metal alcoholate or alkali metal phenate. This can then be reacted with the corresponding alkyl halide, sulfonate or dialkyl sulfate, advantageously in an inert solvent, such as. B. acetone, 1,2-dimethoxyethane, DMF or dimethyl sulfoxide or with an excess of aqueous or aqueous-alcoholic NaOH or KOH at temperatures between about 20 ° and 100 °.

Compounds of the formula Ia are particularly preferred

in which R ¹ , Z ¹ , Z ² and R ^{2 have} the meanings given, m is 1 or 2 and L ¹ and L ^{2 are} each, independently of one another, H or F. In the case of m = 2, the two radicals Z ^{1 are} identical or different. ^{Preferably at least one of the radicals Z 1} and Z ² present in the molecule of the formula Ia is different from the single bond and is preferably -CH ₂ CH ₂ -, -C∼C- or -CO-O-.

Based on the purchasable

the compounds can be represented by methods known per se. In addition to the linkage options listed in the scheme below, there are also analogous synthetic processes via Friedel-Crafts acylation or Wittig reaction with subsequent reduction or hydrogenation for the synthesis of the CH ₂ —CH ₂ linked substances.

the

Compounds containing can be admitted by chlorination using PCl ₅

and subsequent HCl elimination using a base to convert it into the acetylenes. The transformation of the -CH = CH- bridged substances that can be produced via Heck coupling or Wittig reaction succeed in a conventional manner, for. B. by means of bromination and double elimination of HBr.

The introduction of the carboxylate group succeeds in analogy to the introduction of the CH ₂ CH ₂ group (cf. Compound 7, formula scheme below) by means of CO ₂ . The acids formed as intermediates can be esterified with the corresponding phenols, which can be prepared from 1 according to synthesis step ba.

The connection 8 can be implemented according to d) to 12 and analogously to e) to 13. 12 is made using vinyl bromide according to bc) and 13 converted to 14 by means of divinyl zinc according to c). 15 can be derived from FIGS. 12 and 1 by means of cross coupling according to FIG h) obtained or from 13 and 3 by cross coupling.

Through a suitable combination of building blocks 1-15, all precursors of Ia can be built in which Z is C∼C or the single bond. The CH = CH grouping can be converted into the CH ₂ —CH ₂ or —C∼C grouping.

The introduction of the end grouping

succeeds either by using a coupling step with

or by introducing R ² into compounds with the end grouping

The preparation of compounds likewise containing the CO ₂ and / or C∼C intermediate members can be carried out in accordance with analogous formula schemes.

The liquid-crystalline media according to the invention preferably contain one or more inven compounds according to the invention as further constituents 2 to 40, in particular 4 to 30 components. Quite These media particularly preferably contain one or more compounds 7 according to the invention up to 25 components. These further constituents are preferably selected from nematic or nematogenic (monotropic or isotropic) substances, in particular substances from the azoxy classes benzenes, benzylidene anilines, biphenyls, terphenyls, phenyl or cyclohexyl benzoates, cyclohexane carboxylic acid phenyl or cyclohexyl ester, phenyl or cyclohexyl ester of cyclohexylbenzoic acid, phenyl or cyclohexane exyl ester of cyclohexylcyclohexanecarboxylic acid, cyclohexylphenylester of benzoic acid, cyclohexanecar bonsäure, or the cyclohexylcyclohexanecarboxylic acid, phenylcyclohexanes, cyclohexylbiphenyls, phenylcycloh exylcyclohexane, cyclohexylcyclohexane, cyclohexylcyclohexene, cyclohexylcyclohexylcyclohexene, 1,4-bis-cy clohexylbenzenes, 4,4'-bis-cyclohexylbiphenyls, phenyl- or cyclohexylpyrimidines, phenyl- or cyclohexylpyri dine, phenyl or cyclohexyldioxane, phenyl or cyclohexyl-1,3-dithiane, 1,2-diphenylethane, 1,2-dicycloh exylethane, 1-phenyl-2-cyclohexylethane, 1-cyclohexyl-2- (4-phenyl-cyclohexyl) -ethane, 1-cyclohexyl-2-biphe nylylethanes, 1-phenyl-2-cyclohexylphenylethanes, optionally halogenated stilbenes, benzylphenyl ethers, To lane and substituted cinnamic acids. The 1,4-phenylene groups in these compounds can also be fluorinated be.

The most important compounds that can be considered as further constituents of media according to the invention can be characterized by the formulas 1, 2, 3, 4 and 5:

R'-LER "(1)

R'-L-COO-ER "(2)

R'-L-OOC-ER "(3)

R'-L-CH ₂ CH ₂ -ER "(4)

R'-L-C∼C-E-R "(5)

In the formulas 1, 2, 3, 4 and 5, L and E, which can be the same or different, are each independently from one another a divalent radical from the group consisting of -Phe-, -Cyc-, -Phe-Phe-, -Phe-Cyc-, -Cyc-Cyc-, -Pyr-, -Dio-, -G-Phe- and -G-Cyc and their mirror images formed group, with Phe unsub Substituted or fluorine-substituted 1,4-phenylene, Cyc trans-1,4-cyclohexylene or 1,4-cyclohexenylene, Pyr-pyrimidin-2,5-diyl or pyridin-2,5-diyl, Dio 1,3-dioxane-2,5-diyl and G 2- (trans-1,4-cyclohexyl) -ethyl, Pyrimi din-2,5-diyl, pyridine-2,5-diyl or 1,3-dioxane-2,5-diyl.

Preferably one of the radicals L and E is Cyc, Phe or Pyr. E is preferably Cyc, Phe or Phe-Cyc. The media according to the invention preferably contain one or more components selected from the Compounds of the formulas 1, 2, 3, 4 and 5, wherein L and E are selected from the group Cyc, Phe and Pyr and at the same time one or more components selected from the compounds of the formulas 1, 2, 3, 4 and 5, wherein one of the radicals L and E is selected from the group Cyc, Phe and Pyr and the other radical is selected is from the group -Phe-Phe-, -Phe-Cyc-, -Cyc-Cyc-, -G-Phe- and -G-Cyc-, and given optionally one or more components selected from the compounds of the formulas 1, 2, 3, 4 and 5, in which the radicals L and E are selected from the group -Phe-Cyc-, -Cyc-Cyc-, -G-Phe- and -G-Cyc-.

R 'and R "in the compounds of the sub-formulas 1a, 2a, 3a, 4a and 5a each independently denote alkyl, alkenyl, alkoxy, alkenyloxy or alkanoyloxy with up to 8 carbon atoms. In most of these compounds, R' and R" are mutually exclusive different, one of these radicals is usually alkyl or alkenyl. In the compounds of sub-formulas 1b, 2b, 3b, 4b and 5b, R "denotes -CN, -CF ₃ , F, Cl or -NCS; R has the meaning given for the compounds of sub-formulas 1a to 5a and is preferably alkyl or However, other variants of the intended substituents are also used in the compounds of the formulas 1, 2, 3, 4 and 5. Many such substances or mixtures thereof are commercially available .

In addition to components from the group of compounds 1a, 2a, 3a, 4a and 5a (group 1), the media according to the invention preferably also contain components from the group of compounds 1b, 2b, 3b, 4b and 5b (group 2), their proportions preferably are as follows:
Group 1: 20 to 90%, especially 30 to 90%,
Group 2: 10 to 80%, especially 10 to 50%,
the sum of the proportions of the compounds according to the invention and the compounds from groups 1 and 2 being up to 100%.

The media according to the invention preferably contain 1 to 40%, particularly preferably 5 to 30% compounds according to the invention. Media containing more than 40%, in particular 45%, are also preferred up to 90% of compounds according to the invention. The media preferably contain three, four or five inventions proper connections.

The media according to the invention are produced in a conventional manner. Usually the Components dissolved in one another, expediently at elevated temperature. With suitable additives, the liquid-crystalline phases are modified according to the invention so that they are in all previously known Types of liquid crystal display elements can be used. Such additives are the expert known and described in detail in the literature (H. Kelker / R. Hatz, Handbook of Liquid Crystals, Verlag Chemie, Weinheim, 1980). For example, pleochroic dyes can be used to produce colored guest Host systems or substances for changing the dielectric anisotropy, the viscosity and / or the Orientation of the nematic phases are added.

The following examples are intended to illustrate the invention without limiting it. Above and below, percentages mean percentages by weight. All temperatures are given in degrees Celsius. Melting point means melting point, Kp = clearing point. Furthermore, K = crystalline state, N = nematic phase, S = smectic phase and I = isotropic phase. The data between these symbols represent the transition temperatures. Δn means optical anisotropy (589 nm, 20 ° C) and the viscosity (mm ² / sec) was determined at 20 ° C.

"Customary work-up" means: if necessary, water is added, the mixture is extracted with methylene chloride, diethyl ether or toluene, the organic phase is separated off, dried, evaporated and the product is purified by distillation under reduced pressure or crystallization and / or chromatography. The following abbreviations are used:
DAST diethylaminosulfur trifluoride
DCC dicyclohexylcarbodiimide
DDQ dichlorodicyanobenzoquinone
DIBALH diisobutyl aluminum hydride
KOT potassium tertiary butoxide
THF tetrahydrofuran
pTSOH p-toluenesulfonic acid
TMEDA tetramethylethylenediamine

Example 1 (comparative example)

A mixture of 9.2 g of 2,6-difluoro-4- [2- (p-ethoxyphenyl) ethyl] phenylboronic acid (prepared by reacting 3,5-difluorobenzaldehyde with p-ethoxybenzyltriphenylphosphonium iodide according to Wittig and subsequent hydrogenation of the obtained styrene derivative on Pd / C), 6.0 g of 1-bromo-4-n-propylbenzene, 38 ml of 2 ml of aqueous Na ₂ CO ₃ solution., 0.6 g of tetrakis (triphenylphosphine) palladium (0) and 75 ml of toluene is refluxed for two hours. The aqueous phase is extracted twice with toluene and extracted with the org. Phase united. Customary aqueous work-up and chromatographic purification of the residue gives 4- [2- (p-ethoxyphenyl) ethyl] -2,6-difluoro-4'-n-propylbiphenyl.

Example 2 to 51

The following according to the invention are obtained analogously from the corresponding precursors of the formula II Links; Compounds according to the invention are marked with "E".

Claims (7)

1. Liquid-crystalline medium with at least two liquid-crystalline components, characterized in that it contains at least one 1,4-disubstituted 2,6-difluorobenzene compound of the formula I.
wherein
R ¹ H or an unsubstituted or one at least monosubstituted by halogen or alkyl or alkylene radical having 1 to 15 carbon atoms, one or more CH ₂ groups in each of these radicals also being carried out independently of one another
can be replaced in such a way that O atoms are not directly linked to one another,
R ^{2 is} an alkyl or alkylene radical with 1 to 15 carbon atoms that is at least monosubstituted by halogen, and one or more CH ₂ groups in these radicals are each independently of one another
can be replaced in such a way that O atoms are not directly linked to one another,
A ¹ and A ² each independently have one

• a) trans-1,4-cyclohexylene radical, in which one or more non-adjacent CH ₂ groups can also be replaced by -O- and / or -S-.
• b) 1,4 phenylene radical, in which one or two CH groups can also be replaced by N.
• c) A remainder from the group consisting of 1,4-cyclohexenylene, 1,4-bicyclo (2,2,2) octylene, piperidine-1,4-diyl, naphthalene-2,6-diyl, decahydronaphthalene-2,6-diyl and 1,2,3,4-tetrahydronaphthalene-2,6-diyl,

where the radicals (a) and (b) can be substituted by CN or fluorine,
Z ¹ and Z ² each independently of one another -CO-O-, -O-CO-, -CH ₂ O-, -OCH ₂ -, -CH ₂ CH ₂ -, -CH = CH-, -C∼C- or a single bond,
m and n each independently of one another 0, 1 or 2, where
(m + n) is 1, 2 or 3,
with the proviso that at least one of the radicals A ¹ and A ^{2 present in the molecule} means,
contains. 2. Liquid-crystalline medium according to claim 1, characterized in that in the compound of the formula IR ^{1 is} alkyl or alkoxy. 3. Liquid-crystalline medium according to claim 1 or 2, characterized in that it contains compounds of the sub-formulas Ia to If
R ¹ -A ³ -A ² -R ² (Ia)
R ¹ -A ³ -Z ² -A ² -R ² (Ib)
R ¹ -A ³ -Z ² -A ² -Z ² -A ² -R ² (Ic)
R ¹ -A ¹ -Z ¹ -A ³ -Z ² -A ² -R ² (Id)
R ¹ -A ¹ -Z ¹ -A ⁴ -Z ¹ -A ³ -R ² (Ie)
R ¹ -A ⁴ -Z ¹ -A ¹ -Z ¹ -A ³ -R ² (If)
wherein
R ¹ , R ² , A ¹ , Z ¹ , A ² and Z ^{2 have} the meaning given in claim 1,
A ^{3 is} a radical of the formula
and
A ^{4 is} a radical of the formula
means,
contains. 4. Liquid-crystalline medium according to one of claims 1 to 3, characterized characterized in that the medium contains 1 to 40% of the compounds of the Formula (I) contains. 5. Liquid crystal display element, characterized in that it is a liquid-crystalline medium according to claim 1. 6. Electro-optical display element, characterized in that it is used as Dielectric contains a liquid-crystalline medium according to claim 1. 7. 1,4-disubstituted 2,6-difluorobenzene compound of the formula I.
wherein
R ¹ H or an unsubstituted or one at least monosubstituted by halogen or alkyl or alkylene radical having 1 to 15 carbon atoms, one or more CH ₂ groups in each of these radicals also being carried out independently of one another
can be replaced in such a way that O atoms are not directly linked to one another,
R ^{2 is} an alkyl or alkylene radical with 1 to 15 carbon atoms that is at least monosubstituted by halogen, and one or more CH ₂ groups in these radicals are each independently of one another
can be replaced in such a way that O atoms are not directly linked to one another,
A ¹ and A ² each independently have one

• a) trans-1,4-cyclohexylene radical, in which one or more non-adjacent CH ₂ groups can also be replaced by -O- and / or -S-.
• b) 1,4 phenylene radical, in which one or two CH groups can also be replaced by N.
• c) A remainder from the group consisting of 1,4-cyclohexenylene, 1,4-bicyclo (2,2,2) octylene, piperidine-1,4-diyl, naphthalene-2,6-diyl, decahydronaphthalene-2,6-diyl and 1,2,3,4-tetrahydronaphthalene-2,6-diyl,

where the radicals (a) and (b) can be substituted by CN or fluorine,
Z ¹ and Z ² each independently of one another -CO-O-, -O-CO-, -CH ₂ O-, -OCH ₂ -, -CH ₂ CH ₂ -, -CH = CH-, -C∼C- or a single bond,
m and n each independently of one another 0, 1 or 2, where
(m + n) is 1, 2 or 3,
with the proviso that at least one of the radicals A ¹ and A ^{2 present in the molecule}
means.