Directed tridentate Lewis acids based on the 1,3,5-trisilacyclohexane skeleton with three ethynyl groups [CH2Si(Me)(C2H)]3 were synthesised and functionalised by hydroboration with HB(C6F5)2, yielding the ethenylborane {CH2Si(Me)[C2H2B(C6F5)2]}3, and by metalation with gallium and indium organyls affording {CH2Si(Me)[C2M(R)2]}3 (M = Ga, In, R = Me, Et). In the synthesis of the backbone the influence of substituents (MeO, EtO and iPrO groups at Si) on the orientation of the methyl group was studied with the aim to increase the abundance of the all-cis isomer. New compounds were identified by elemental analyses, multi-nuclear NMR spectroscopy and in some cases by IR spectroscopy. Crystal structures were obtained for cis-trans-[CH2Si(Me)(Cl)]3, all-cis-[CH2Si(Me)(H)]3, all-cis-[CH2Si(Me)(C2H)]3, cis-trans-[CH2Si(Me)(C2H)]3 and all-cis-[CH2Si(Me)(C2SiMe3)]3. A gas-phase electron diffraction experiment for all-cis-[CH2Si(Me)(C2H)]3 provides information on the relative stabilities of the all-equatorial and all-axial form; the first is preferred in both solid and gas phase. The gallium-based Lewis acid {CH2Si(Me)[C2Ga(Et)2]}3 was reacted with a tridentate Lewis base (1,3,5-trimethyl-1,3,5-triazacyclohexane) in an NMR titration experiment. The generated host-guest complexes involved in the equilibria during this reaction were identified by DOSY NMR spectroscopy by comparing measured diffusion coefficients with those of the suitable reference compounds of same size and shape.

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The 1,3,5-trisilacyclohexane skeleton [CH2Si(Ph)(C2H)]3 equipped with three ethynyl groups was synthesised and functionalised to afford tridentate Lewis acids with directed functions. Hydroboration with HB(C6F5)2 yielded the ethenylborane {CH2Si(Ph)[C2H2B(C6F5)2]}3, while metalation with gallium organyls afforded {CH2Si(Ph)[C2Ga(R)2]}3 (R = Me, Et). The new compounds were identified by elemental analyses, multi-nuclear NMR spectroscopy and IR spectroscopy. Crystal structures were obtained for all-cis-[CH2Si(Ph)(OMe)]3, cis-trans-[CH2Si(Ph)(Cl)]3, all-cis-[CH2Si(Ph)(H)]3 and all-cis-[CH2Si(Ph)(C2H)]3.

Abstract.1,1,3,3,5,5-Hexavinyl-1,3,5-trisilacylohexane [Si(CH=CH 2 ) 2 CH 2 ] 3 was synthesized and hydrosilylated with trichlorosilane to afford the first generation of a dendrimer. Conversion of this molecule with 18 Si-Cl functions on its surface with an excess of vinylmagnesium bromide yielded the 18-fold vinylated dendrimer.