Neutral Hexacoordinate Mixed Trichelate Silicon Complexes, Structure and Stereodynamics†

Neutral hexacoordinate silicon trichelates have been synthesized by transsilylation, using two approaches: (i) The reaction of a dichloro-monocyclic silane [2,5-diphenyl-2,5-diazasilolidine] with two mol-equivalents of O-(trimethylsilyl)imidates. (ii) A dichloro-dichelate reacted with one mol-equivalent of the trimethylsilyl bidentate ligand precursor, bis(trimethylsilyl)benzhydroxamic acid imidate. The former group of complexes underwent inversion of configuration observed by the temperature dependence of the 1H NMR spectra and coalescence of signals due to diastereotopic N-methyl- and CH2 groups, presumably by exchange of hydrazido chelate rings through a bicapped tetrahedral intermediate or transition state. The activation free energies range between 13.8 and 14.7 kcal·mol–1. Similar exchange in the hydroxamic acid derived complexes was not observed, because of much shorter and stronger dative N–Si bonds.