Bildung siliciumorganischer Verbindungen. 96. Bildung und Struktur von P-Yliden des 1,3,5-Trisilacyclohexans (Einfluß der Substituenten)

Formation of Organosilicon Compounds. 96. Preparation and Structure of P-Ylides of the 1,3,5-Trisilahexanes (Influence of the Substituents) The influence of the substituents at the silicon atoms on formation and structure of ylides of 1,3,5-trisilacyclohexanesis investigated. The reactions of 1 , 2 , 3 with Me₃Si? PMe₂ lead via cleavage of the Si? P bond and subsequent rearrangement to the ylides 4 , 5 and 6 . The x-ray structure determination reveals, that the atoms of the ylid part of 4 are in a plane with the shortened bond distances d(C? P) = 168.6 pm and d(Si? C) = 180.1 pm, whereas the other endocyclic Si? C distances remain nearly unaffected by the ylid formation. Only the endocyclic bond angles C? Si? C of the Si atoms of the ylid are enlarged (116°). In the molecule 6 d(C? P) = 164.6 pm is much shorter, but d(P? Br) = 236.6 pm is enlarged. This enlargement is coupled with a deviation of 17 pm for the ylidic C atom from the ylid plane. Distances and angles are normal in the methylated trisilnhexane. The ring in 6 has boat conformation, in 4 a flat chair conformation.