Synthesis and reactions of neutral hypercoordinate allylsilicon compounds having a tropolonato ligand

A novel intramolecular allylic migration from silicon to carbon was observed during the reaction of allylmethyldichlorosilane with tropolone in the presence of triethylamine-to give an isomeric mixture of pentacoordinate silicon compounds having allylated tropolonato Ligand. The molecular structure of the major isomer was determined by X-ray analysis. Reaction of diprenyldichlorosilane with tropolone at low temperature (-35 degrees C) gave the first hexacoordinate allylsilicon compound, diprenylbis(tropolonato)silicon, which underwent the allylic migration at room temperature to give the neutral pentacoordinate allylic silicon compound. The activation parameters for the rearrangement in CDCl3 were determined by NMR to be Delta H-not equal = 77.6 kJ/mol and Delta S-not equal = -60.3 J/(mol . K). Facile allylation of aldehyde was performed with the neutral pentacoordinate allylic silicon compounds to give the corresponding homoallylic alcohols in good yields (70-90%) at room temperature without any catalyst.