Organosilylalkyl or organosilylalkenyl compounds, process for preparing them and their use in liquid-crystalline mixtures

A liquid-crystalline silyalkyl or silyalkenyl compound of the general formula (I) ##STR91## in which R.sup.1 denotes straight-chain or branched alkyl or alkenyl (with or without asymmetrical carbon atom) containing 2 to 16 carbon atoms, it also being possible for one or two nonadjacent --CH.sub.2 --groups to be substituted by --O--, --S--, --CO--O--, or --O--CO-- and for hydrogen to be replaced by fluorine, or one of the following radicals ##STR92## A.sup.1,A.sup.2,A.sup.3 denote, identically or differently, 1, 4-phenylene in which 1 or 2 hydrogens may be replaced by fluorine, trans-1,4-cyclohexylene pyridine-2,5-diyl, pyrimidine-2,5-diyl, 1,3,4-thiadiazol-2,5-diyl, 1,3-dioxane-2,5-diyl,

• M.sup.1, M.sup.2 denote, identically or differently, CO--O, O--CO, CH.sub.2 --O, O--CH.sub.2,
• G, G.sup.1 denotes straight-chain alkylene containing 1 to 16 carbon atoms in which one or two nonadjacent --CH.sub.2 -- groups may also be replaced by --O--, --O--CO--, or --CO--O--, with the proviso that Si is bound only to a carbon which has hydrogen and/or carbon as adjacent atoms,
• R.sup.2, R.sup.3, R.sup.4, R.sup.5 denote hydrogen or a straight-chain alkyl containing 1 to 16, in which a --CH.sub.2 -- group may also be replaced by cyclic alkyl containing 3 to 8 carbon atoms,
• R.sup.6, R.sup.7, R.sup.8 denote straight-chain alkyl containing 1 to 16 carbon atoms or cyclic alkyl containing 3 to 8 carbon atoms,
• j, k, l, m, n denote 0 or 1,
• with the proviso that j+l+n=2 or 3.