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Dicyclohexylammonium salts of bis(1,2 catecholato O,O´) [(N methylacetamido)methyl C,O]silicate and bis(1,2 catecholato O,O´) [(2 oxohexahydroazepin 1 yl)methyl C,O]silicatewere synthesized by the transesterification of the corresponding trimethoxysilyl derivatives by pyrocatechol in the presence of dicyclohexylamine. According to the X ray diffraction data, the synthesized salts are the anionic silicon complexes, in which the Si atoms are six coordi nate due to two (O,O´) dianionic and one (C,O) monoanionic chelate ligands. In the latter, chelating occurs due to the formation of the intramolecular (intraionic) coordination bond O→Si.The structures of more than 40 salts containing organo silicon anionic complexes with the hypercoordinated Si atom have been studied to the present time. 1a-c The most of them are two charge tris chelate complexes with (O,O´) dianionic ligands. Examples of zwitterionic com pounds with (N,О) dianionic ligands are also known. 2a-e The tris chelates described in the literature are character ized by the symmetric structure approximately corre sponding to the point symmetry group С 3 , and the coordi nation mode of the Si atom has the configuration of a slightly distorted octahedron. The most abundant anion in these compounds is tris(catecholato О,О´)silicate [Si(cat) 3 ] 2-(1, cat is the catecholate dianion), and the O-Si bond lengths in its studied salts vary in a rather narrow interval (1.76-1.81 Å). 1aNote that complexes with various chelate ligands are almost absent among the chelates described. The exceptions are zwitterionic silicate 2 (see Ref. 2c) and biscatecholate complexes with the N→Si coordination, for instance, compound 3 (see Ref. 3a).Continuing our investigations 4 of the influence of the environment of the silicon atom on the degree of possible intramolecular bonding O→Si due to the amidic oxygen atom in the neutral and cationic complexes of hyper coordinated silicon and Si substituted N (silylmethyl) amides and N (silylmethyl)lactams, in the present work we synthesized and studied by X ray diffraction analysis * Dedicated to B. A. Trofimov on the occasion of his 70th anniversary.

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367ChemInform Abstract (4 refs.).