6p-electron Aromatic Species Containing Heavy Group 14 Elements: Synthesis, Structure and Reactivity of Lithium 1,2,3-Trisilacyclopentadienide

Abstract

Cyclopentadienyl anion is one of the most fundamental 6π-electron aromatic species, however, very few derivatives containing heavier group 14 elements were reported to date. Here, we report the synthesis, structure and reactivity of novel heavy cyclopentadienide.
The heavy analogue of CpLi, lithium 1,2,3-trisilacyclopentadienide, was synthesized by the reduction of 1,2,3-trisilacyclopenta-1,4-diene with KC₈ followed by the treatment with excess of dry LiBr. Then, the ligand exchange reaction of the anion from THF to O=C^tBu₈ resulted in the formation of ketone-coordinated lithium 1,2,3-trisilacyclopentadinide. All NMR signals and the crystal structure indicated the existence of the significant delocalization of π-electrons in five-membered ring. The complexation of lithium 1,2,3-trisilacyclopentadienide with 12-crown-4 or the reaction with [Cp*RuCl]₄ gave Li-free cyclic disilenide and heavy ruthenocene analogue, respectively.