Spirosilicates zwitterionic

The zwitterion X5-spirosilicate bis[2,3-naphthalendiolato][2-(dimethylammonio)phe-nyl]silicate (56 isolated as 57 = 56-1/2 MeCN) was synthesized by reaction of [2-(dimethylamino)phenyl]dimethoxyorganosilanes with 2,3-dihydroxynaphthalene in acetonitrile at room temperature. Reaction of 57 or of [2-(dimethylamino)phenyl]trimetho-xysilane with water in acetonitrile yielded the cage-like silasesquioxane 58 (R = 2 — Me2NCgH4). The crystal structures of 57 and 58 were studied by X-ray diffraction. In addition, 57 and 58 were characterized by solid-state 29Si CPMAS NMR142 (Figure 34). 

The crystal structures of several members of the zwitterionic complex family were determined. Like in the anionic spirosilicates, the structures were found to vary continuously between TBP and SP, with Si—O bond lengths essentially equal to those in anionic analogs. More than one crystalline modification was found for some of the zwitterions, and even those (even for the same complex ) were substantially different in molecular geometry for 60 the percent deviation from TBP - SP was calculated to be 34.9% in the monoclinic crystal, 70.0% in the orthorombic, 86.2% in the crystalline hydrate and 96.3% in another crystal form of the monohydrate46 47. These results were interpreted in terms of variation in hydrogen bonds in the different crystal modifications. In the hydrates... 

The preparation of a novel neutral zwitterionic k5-spirosilicate and its characterization was reported238. 

The short reaction time, the mild reaction conditions as well as the high yields and the selectivity proved the hydrolytic oligocondensation of zwitterionic A, -spirosilicates to be an appropriate method for the synthesis of organo-functionalized octasilsesquioxanes [5]. The synthesis of 1 required a modification of the reaction conditions and an extension to ionic A, -spirosilicates. 

Unusual selectivities have sometimes been observed in the displacement reactions leading to zwitterions equation 17 shows a case of inverse selectivity , in which the aminoalkyl group is displaced, rather than the phenyl, leading to an anionic spirosilicate. ... 

Dinuclear zwitterionic spirosilicates were also synthesized and characterized by Tacke and coworkers (equations 22 and 23). These differ from previous dinuclear silicates in that they are bis-zwitterionic. The bridge in 87 is through the covalent bonding of a l,4-(dimethylene)piperazine, whereas in equation 23 a double bridge is formed by two tetradentate ligand molecules, tartaric acid. The crystal structure of 87 proved that the product was the meso compound, with opposite configurations at the silicon centers . When the reaction in equation 23 was run with optically active (l ,J )-(+)-tartaric acid the first optically active zwitterionic bis-silicate (88) was obtained . 

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