Penta- and hexacoordinate silicon mixed dichelates with the SiC ₂O₂N(Cl) ligand environment

New dichelate complexes of silicon with different chelate rings have been prepared by transsilylation, using ClCH₂SiMeCl₂ and various N- and O-TMS-hydrazides and amides. Their structures and possible transformations between penta and hexacoordinate complexes have been studied. Many of the complexes are pentacoordinate ionic chloride salts, with charges on an ammonium nitrogen or on silicon. Compounds 5a,b have a zwitterionic aminimide structure, with a possible additional positive charge on silicon. 12 Is the only compound in the series in which penta- hexacoordinate complex exchange is found, involving reversible non-ionic N-Si bond dissociation. 16 is the first reported mixed dichelate siliconium-ion salt with two O→Si dative bonds. Its structure, as well as that of 5a, is established by crystallographic analysis.