Adjusting the Number of Functional Groups in Vicinal Bis(trichlorosilylated) Benzenes

Organo(chloro)silanes are essential chemicals, but the synthesis of compounds of the formula R_nSiCl_4-n with defined values of n is usually laborious. Herein, we first disclose that a [4+2]-cycloaddition between readily available Cl₃SiC≡CSiCl₃ and selected dienes provides facile access to vicinal bis(trichlorosilylated) benzenes and bicyclo[2.2.2]octa-2,5-dienes. Second, we show how the number of six Si-Cl bonds in 1,2-(Cl₃Si)₂C₆H₂Me₂ (1) can be selectively reduced to four or two by reaction with pinacol (H₂pin) or catechol (H₂cat), which act as Si⋅⋅⋅Si'-bridging and/or Si-chelating ligands. Third, we demonstrate that the thermolysis of compound 6, which contains a benzannulated eight-membered C₂(SiCl₂)₂(μ-pin) ring with Si⋅⋅⋅Si'-bridging pin moiety, furnishes 13 with a benzannulated five-membered C₂(SiCl₂)₂O ring via the release of pinacolone. Such cyclic disiloxanes are valuable building blocks for specialty silicones; an alternative assembly of the Si-O-Si unit by controlled hydrolysis of 1 is not feasible if the four valuable Si-Cl functionalities are to be retained for further derivatization. Substitution of one Cl atom per Si site of 13 gives the rac-1,3-disila-2-oxaindane rac-15 with high selectivity.