Bis-chelates with the Dimethylamino Donor Group

The most widely studied group of hydrazide-based silicon complexes is the group of neutral hexacoordinate bis-chelates, with coordination of two dimethylamino donors to silicon. 

29Si NMR Chemical Shifts of Neutral Hexacoordinate Bis-(N Si) Silicon Complexes with the N-NMe2 Donor Group [CDC13, 300 K, ( /, Hz)] 

In contrast, the reaction of 1 with polyfluorosilanes (26) proceeded slowly at room temperature (over several hours).16 Indeed, in this reaction the neutral pentacoordinate complex resulting from a single ligand exchange (4 a-c,h) was formed as a stable intermediate and could be observed for several hours in the NMR spectra (Eq. 16). 

The question arose as to which complexes formed octahedral and which bicapped-tetrahedral molecular structures. In the bicapped-tetrahedral complexes 39-42, the number of electronegative ligands attached to silicon is smaller than in the octahedral complexes (30-38). A maximum of one Si-C bond is allowed in the octahedral complexes. When the number is greater than one, bicapped tetrahedral geometries are obtained in the solid-state. 

Selected Bond Lengths (A) and Angles (deg.) for Complexes of Series 30-38, 54 

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