Abstract
Controlled condensation reactions of tertiary silanetriols CH3(CH2)n(CH3)2CSi(OH)3 (1b–f; n = 1–5) in the presence of trifluoroacetic acid and the hydrolysis of CH3(CH2)6(CH3)2CSiCl3 (3) lead to the selective formation of the corresponding disiloxane tetrols [CH3(CH2)n(CH3)2CSi(OH)2]2O (2b–g; n = 1–6) in good yields. The TBAF-driven condensation reactions of the silanetriols CH3(CH2)n(CH3)2CSi(OH)3 (1a–c; n = 0–2) as well as of the disiloxane-1,1,3,3-tetrol 2d (n = 3) yield in the selective formation of the first T8 cages bearing tertiary carbon substituents, CH3(CH2)n(CH3)2C (4a–d; n = 0–3), which was not possible via the condensation of their alkoxysilane counterparts so far. The resulting compounds 2b–g and 4a–d have been characterized by multinuclear NMR, MS, and single-crystal X-ray diffraction.
Highlights
Octasilsesquioxanes T8 (T = RSi(O−)[3] with R = inorganic or organic substituent, H) belong to the class of POSS compounds (POSS = polyhedral oligomeric silsesquioxanes) which have attracted much attention in recent years.[1,2] As hybrid materials with properties of both SiO2 and siloxanes,[3] they enjoy widespread applications for example in catalysis,[4] as model systems for silica surfaces,[5,6] in the design of superoleophobic surfaces,[7] ionic liquids,[8] and biocompatible materials,[9] and in polymer chemistry.[2]
The synthesis of T8 was revolutionized by Bassindale et al, who treated trialkoxysilanes with tetrabutylammonium fluoride (TBAF) in THF, which in many cases led to the selective 95%.10−12 The formation of T8 cages precise mechanism of in yields of up POSS formation to is complex and is still under investigation
The synthesis of T6 cages from their corresponding silanetriol counterparts has already been described by Unno et al and in our laboratories using multistep procedures.[14−16] we wanted to investigate whether a one-pot synthesis starting from silanetriols works well as the classical TBAF procedure established by Bassindale et al, which starts from alkoxysilanes
Summary
The intermediate formation of the primary hydrolysis products RSi(OH)[3] has been postulated starting from trichlorosilanes.[13] The synthesis of T6 cages from their corresponding silanetriol counterparts has already been described by Unno et al and in our laboratories using multistep procedures.[14−16] we wanted to investigate whether a one-pot synthesis starting from silanetriols works well as the classical TBAF procedure established by Bassindale et al, which starts from alkoxysilanes. This investigation should shed light on the question of whether silanetriols really do occur as intermediates in the classical TBAF procedure
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