Intramolecular ring expansion of a 2-lithium-anilido-2-fluoro-1,3-diaza- 2silacyclopentene to a l,3,5-Triaza-7-bora-2-silacycloheptene - Experimental and quantum-chemical results [Intramolekulare ringerweiterung eines 2-lithium-anilido-2-fluoro-1,3-diaza- 2-silacyclopentens zum 1,3,5-Triaza-7-bora-2-silacyclohepten Experimentelle und quantenchemische ergebnisse]

摘要

The reaction between, the lithiated 2-diisopropylanilino-2-fluoro-1,3- diaza-2-silacyclopentene, (HCNCMe_3)_2SiFNLi(2,6-Me _2CH)_2C_6H_3 (I), and BF _3OEt_2 in THF afforded in an unknown, intramolecular ring expansion the seven-membered 1,3,4-triaza-7-bora-2-silacycloheptene, (HCNCMe_3(SiF_2)BFN-2,6-(Me_2CH)_2C _6H_3 (1). Starting with the BF_2 substituted compound A, quantum-chemical calculations on the thermal isomeration process revealed a two-step reaction mechanism: First, the bicyclic compound C is fonned via transition state TS1, and second, a 1,3-fluoride ion migration occurs in the seven-membered transition state TS2 from a BF_2- to a SiF-unit. The reaction mechanism and the structures of the transition, states are discussed in detail.