The molecular dynamics and reactivity of tris(inden-1-yl)silane: an NMR spectroscopic and X-ray crystallographic study

Abstract

The synthesis, structural characterisation (NMR, X-ray), molecular dynamics and reactivity of tris(inden-1-yl)silane, 9, are discussed. Spectroscopic data obtained from 2D-EXSY NMR experiments clearly demonstrate that the title compound is stereochemically non-rigid, even at temperatures where line broadening is not evident (ΔG^‡ ≈ 24 kcal mol⁻¹). The dynamic behaviour of 9 is rationalised in terms of successive [1,5]-silicon shifts; indeed, the isoindene intermediates generated in this process have been sequentially trapped by tetracyanoethylene, yielding tris(5,6-benzo-2,2,3,3-tetracyanobicyclo[2.2.1]hept-5-en-7-yl)silane,14. The silane, 9, has been transformed into tris(inden-1-yl)hexylsilane, 19, via hydrosilylation with hex-1-ene in the presence of Wilkinson’s catalyst. Compound 14 was quantitatively converted into the crystallographically characterised tris(5,6-benzo-2,2,3,3-tetracyanobicyclo[2.2.1]hept-5-en-7-yl)silanol, 17, by treatment with water, or into tris(5,6-benzo-2,2,3,3-tetracyanobicyclo[2.2.1]hept-5-en-7-yl)fluorosilane, 22, by the addition of either HBF₄ or Ph₃C⁺PF₆⁻.