of 1-trimethylsilyl-1,3-diaza-2-silacyclopentane, BuLi and MeSiF3. In the synthesis of N-fluorosilyl-1,3-diaza-2-silacyclopentanes constitutionalisomers were formed (30–33). Quantum-chemical calculations support the isomerisation mechanism. An iminosilane with an SiN double bond is the intermediate product of the rearrangement process.