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 0-(trimethylsilyl)imidates, (ii) A dichloro-dishelate 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.