Neutral hydrazide-based hexacoordinate silicon bis-chelates with no halogen ligands, but with two monodentate alkyl (aryl) or hydrido ligands, are described.

Dimethylamino complexes (1) form weakly coordinated "bicapped tetrahedral" geometries in the solid state (Figure 1), while imino-coordinated complexes (2) are more strongly bound and form distorted octahedral structures (Figure 2). The difference in donor strengths of these two nitrogen-donor types determines whether the dative bonds (in 2 and 1, respectively) provide sufficient energy to promote silicon from tetrahedral to octahedral configuration.

Hexacoordinate silacyclobutane complexes (3) have been prepared. Upon mild heating or photolyzing they undergo a skeletal rearrangement involving cleavage of the four-membered heterocycle (4). In the absence of imino α-protons (3, R¹ = Ph, R² = H) addition of the four-membered ring residue to the imino double bond takes place, forming a new chelate ring (5).

Figure 1: Crystal structure of 1	Figure 2: Crystal structure of 2

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