Synthesis and Characterization of Cyclic Silenolates

Based on earlier work by Ottosson [1] and Ohshita [2] the previously unknown cyclic silenolates 1a-c and 2a-b have been synthesized by the reaction of acylcyclohexasilanes with one or two equivalents of KOtBu. The nature of the anions (silenide or silenolate) and consequently the outcome of subsequent reaction steps largely depends on the substituent R at the carbonyl function. Detailed NMR-analysis of 1a-c and 2a-b corroborate this deduction. Furthermore, for 1a-c and 2a-b single crystals which were suitable for X-ray structure analysis could be grown. Very interesting is the reactivity of 1b, which at 50°C undergoes a hitherto unknown 1,4-trimethylsilyl-migration followed by a ring cleavage of the cyclohexasilane cycle to form the anion 3a. The high selectivity of these reactions is demonstrated by the formation of an acyl-functionalized bicyclo-2,2,2-octasilane in >90% yield from 2a and \(ClSiMe_{2}SiMe_{2}Cl\).