TIN-CARBON BOND FORMATION BY SIMPLE ADDITION OF CYCLIC DIENES TO A BIS(AMINO)STANNYLENE - A MECHANISTIC STUDY

The addition of cyclopentadiene and indene to Bu'NSiMe(2)NBu'Sn result ed in the formation of 'adducts' (X-ray structural characterisation) t hrough tin-carbon bonding and hydrogen migration to one of the nitroge n atoms. In the cyclopentadienyl compound pi bonding is observed (Sn-C 2.47-2.76 Angstrom) whereas the indenyl derivative displays a sigma-b ond (Sn-C 2.343 Angstrom). In a similar reaction of Bu'NSiMe(2)NBu'E ( E = Ge or Pb) with cyclopentadiene either the starting compounds or pl umbocene along with an amine were isolated. At room temperature the re action between indene and the cyclic stannylene is an equilibrium, the rate constants of which were raised by a factor of 3.0 for the associ ation and slowed by a factor of 4.2 for the dissociation when deuteria ted indene was used. From the kinetic data, a concerted addition mecha nism of the proton and the indenyl group is favoured over an ionic two -step mechanism. If the steric hindrance of the protic cyclic diene sy stem is raised (pentamethylcyclopentadiene) no reaction between the st annylene and diene is observed.