Siliciumverbindungen mit starken intramolekularen sterischen Wechselwirkungen: XLIV. [4 + 1]- versus [4 + 2]-Cycloadditionen von Di-t-butylsilylen und Tetra-t-butyldisilen an 1,4-Diazabutadiene

Abstract

Photolysis of hexa-t-butylcyclotrisilane in the presence of several 1,4-dialkyl-1,4-diaza-1,3-butadienes leads to addition of tetra-t-butyldisilene to the nitrogen atoms in a [2 + 4]-fashion to give the corresponding 1,4-diaza-2,3-disila-5-cyclohexenes. The X-ray structure analysis of the 1,4-dicyclohexyl derivative ( 15) reveals a very long SiSi bond distance of 246.9(1) pm within the strained six-membered ring. 1,3-Diaza-2-sila-4-cyclopentenes are accessible by reaction of 1,4-diaza-1,3-butadienes with lithium and di-t-butyldichlorosilane or by a [4 + 1]-cycloaddition with di-t-butylsilylene, generated photolytically from 1,1-di-t-butyl- trans-2,3-dimethylsilirane. The X-ray structure analysis of the 1,3-dicyclohexyl derivative ( 18) shows a nearly planar five-membered ring. An interesting structural feature of 15 and 18 is the planar arrangement of carbon and silicon atoms around each nitrogen atom.