Dimerization of a marginally stable disilenyl germylene to tricyclic systems: evidence for reversible NHC-coordination

Abstract

Tetrasiladigermatricyclohexanes in two isomeric forms (chair and doubly-bridged tetrahedron) are obtained by the reaction of MeLi with an α-chlorosilyl functionalized NHC-stabilized silagermenylidene. ²⁹Si NMR at low temperature proves the initial formation of a monomeric NHC-adduct of a disilenyl germylene followed by cyclisation to the isomeric heavy cyclopropene. Addition of an excess of NHC stabilizes the both intermediates and demonstrates the reversibility of rate-determining initial equilibria involving NHC dissociation. Finally, a mixture of two isomeric tricyclic Si₄Ge₂ species is obtained: at elevated temperature the chair isomer converts to the doubly edge-bridged tetrahedron.