Cage silsesquioxanes

The self-organization of polysilanols in the presence of other hydrogen bond acceptors has been studied by several groups.512-516 Several other publications have dealt with the stepwise synthesis of siloxane and siloxanol chains.450,517-522 Recent work on fully condensed siloxane rings and silsesquioxane cages involves the non-aqueous hydrolysis of chlorosilanes - as well as mechanistic and structural studies. 

No fully characterized metallasilsesquioxane derivatives of Mn, Tc or Re have been reported until now. It has been reported that reactions of 2 or 3 with rhe-nium(VII) precursors are complicated and often result in dehydration of the silsesquioxane cage without incorporation of rhenium.Recently it has been found... 

Fig. 1. Octa-, deca-, and dodeca-silsesquioxane cage-types...

The retention times are 8.2 min for [Cl-(CH2)3]g(SiOi 5)5, 16.0 min for [Cl-(CH2)3],o(SiOi 5)10 and 37.4 min for [Cl-(CH2)3]i2(SiOi 5)12 at 7 mL min flow rate. The substitution of the chlorine atoms at octa [(3-chloropropyl)-silsesquioxane] by acetoxy- or cyano groups is possible by using potassium acetate or sodium cyanide and 18-crown-6 as phase transfer catalyst in acetonitrile. In addition to the observed substitution, partial rearrangement to the greater deca- and dodeca-silsesquioxane cages, also took place. 

An unprecedented functional Yb silsesquioxane was obtained as outlined in Scheme 29.12. Trisilanol 1 was lithiated in situ using an excess of LiN(SiMe3)2, followed by treatment with YbCfi. In bimetallic 44, a reactive ytterbium bis(trimethylsilyl)amide unit resides on a model silica surface formed by two lithium-linked silsesquioxane cages. 

To make sure that the trapped H atoms derive from the substituents of the silsesquioxane cages, d72-QgM8 was prepared in a multistep procedure starting from CD3MgI [3] and y-irradiated. After being irradiated in the solid state at ambient temperature, it shows the typical EPR spectrum of atomic deuterium, as depicted in Fig. 2b. Up to now, EPR spectroscopy is the only means of detecting trapped H atoms with sufficient sensitivity. 

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