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

Article abstract of DOI:10.1002/zaac.200900341

The reaction between, the lithiated 2-diisopropylanilino-2-fluoro-1,3- diaza-2-silacyclopentene, (HCNCMe₃)₂SiFNLi(2,6-Me ₂CH)₂C₆H₃ (I), and BF ₃OEt₂ in THF afforded in an unknown, intramolecular ring expansion the seven-membered 1,3,4-triaza-7-bora-2-silacycloheptene, (HCNCMe₃(SiF₂)BFN-2,6-(Me₂CH)₂C ₆H₃ (1). Starting with the BF₂ 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 BF₂- to a SiF-unit. The reaction mechanism and the structures of the transition, states are discussed in detail.