NOVEL ZWITTERIONIC LAMBDA-5-SPIROSILICATES - SYNTHESIS AND CRYSTAL-STRUCTURE OF BIS[1,2-BENZENEDIOLATO(2-)][2-(DIMETHYLAMMONIO)PHENYL]SILICATE AND SYNTHESIS OF BIS[2,3-NAPHTHALENEDIOLATO(2-)][2-(DIMETHYLAMMONIO)PHENYL]SILICATE HEMIACETONITRILE SOLVATE

The zwitterionic lambda5-spirosilicates bis[1,2-benzenediolato(2-)][2-(dimethylammonio)phenyl] silicate (4) and bis [2,3-naphthalenediolato(2-)][2-(dimethylammonio)phenyl]silicate (5; isolated as 5.1/2CH3CN) were synthesized and the crystal structure of 4 was studied by X-ray diffraction. 4 was prepared by reaction of [2-(dimethylamino)phenyl]trimethoxysilane (7) or bis[2-(dimethylamino)phenyl]dimethoxysilane (8) with 1,2-dihydroxybenzene in acetonitrile at room temperature. 5 was synthesized analogously by reaction of 7 or 8 with 2,3-dihydroxynaphthalene. The silanes 7 and 8 were obtained by reaction of tetramethoxysilane (6) with [2-(dimethylamino)phenyl]lithium. The reactions 8 --> 4 and 8 --> 5 involve a remarkable Si-C cleavage leading to the formation of (dimethylamino)benzene. The pentacoordinate silicon atoms of 4 and 5 are surrounded by four oxygen atoms and one sp2 hybridized carbon atom. The coordination polyhedron of 4 can be described as a distorted square pyramid, the carbon atom being in the apical position (the structure is distorted by 69,1 % from the trigonal bipyramid towards the square pyramid). In the crystal, 4 forms an intramolecular N-H ... O hydrogen bond.