An improved method has been devised for the preparation of (HSiOs/2)s. The previously unknown higher homologs (HSiOi/,)i0-i6 have also been prepared and characterized. They were isolated from a soluble, silanol-free resin obtained by a rather unusual hydrolysis and condensation procedure whereby water is generated via the sulfonation of an aromatic solvent such as benzene. Evidence for the existence of structural isomerism in the larger cage systems was obtained from nmr studies; i.e., only the octamer and decamer exhibit simple single-line spectra.
Despitethe attention accorded to prismatic silsesquioxane oligomers [(RSiOy2)8,10,12] in recent years,1 relatively little information is available concerning the oligomeric forms of the simplest member of
empirical least-squares treatment of Figure 4 to be 97, 97, and 94°, respectively, while the observed values are 94, 92, and 92°. The Pd-bridge Cl bonds opposite the olefinic groups are 0.1 A longer than the Pd-Cl bond lengths in (PdCl2)". However, the ring angles in all three palladium compounds are the same. This observation can be rationalized by invoking the "trans" effect and requiring the palladium orbitals to be highly directional in character. This can be contrasted to the Ni2Cl84_ anion with a "well-behaved" Ni-Cl-Ni angle of 99.1 °. GaCl3 has a Ga-Cl-Ga angle approximately 5°less than that predicted by the Ga-Cl distance of 2.29 Á. Dahl33 has pointed out that one of the factors leading to anomalously acute bridge angles is metalmetal bonding, and perhaps this is the case in GaCl3.
All of the halogens form single and mixed silicon halides. Monomeric silicon halides and halohydrides are generally tetrahedral compounds. A large number of halogenated polysilanes are also known. The only compounds of industrial importance are tetrachlorosilane and trichlorosilane. Both are used as precursors: the former primarily for high purity fumed silica; the latter for organosilanes and semiconductor‐grade silicon metal. Dichlorosilane, a by‐product of the other chlorosilanes, also finds use in the semiconductor industry.
Ligand redistribution of appropriate alkoxy-or chlorosiloxane substrates at elevated temperatures afforded examples of the title heterocyclic system bearing easily solvolyzable substituents at one or both silicon sites. Also described are novel spirocyclic derivatives of the bidentate alkoxy ligand, -OCMe&H2CH&Mez0-.
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