Neutral hexacoordinate silicon chelates with two chloro ligands (1) have been converted to neutral tris-chelates (6 and 7) by reaction with bis-(O,O-trimethylsilyl)catechol ( 4) and (Z)-Me 3 SiO(Ph)CdNNHSiMe 3 (5), respectively. Likewise, zwitterionic dichloro-hexacoordinate chelate (2a) was converted to the zwitterionic tris-chelate 8 with three different chelate rings, by reaction with 4. 2D-NOESY NMR spectra at various temperatures for 6a and 7a and for the chirally labeled 6b and 7c showed two consecutive ligand-site exchange processes, assigned to interchange of dimethylhydrazido-chelate rings via (O,O)-1,2-shift (6a, ∆G* ) 20.8 kcal mol -1 , 7a, 18.5 kcal mol -1 ) and dissociation-recombination of the N-Si bond. In 8, the NMR evidence shows that the lower process is N-Si dissociation-recombination, followed by enantiomerization at silicon via (O,O)-exchange (∆G* ) 16.1 and 20.9 kcal mol -1 , respectively). † Dedicated to Professor Mikhail Voronkov on the occasion of his 80th birthday.(1) For reviews on hypervalent silicon compounds see: (a) Chuit,
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