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Silicon Hybridization Energy Probed by Changes in Ligand Donor Strength and Molecular Rearrangements in Hexacoordinate Silicon Dichelates

Daniel Kost 1Boris Gostevskii 1Inna Kalikhman 1Mark Botoshansky 2Menahem Kaftory 2

1. Ben-Gurion University, Department of Chemistry, Beer-Sheva 84105, Israel
2. Technion, Department of Chemistry, Haifa 32000, Israel


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).

bg559colorSmall_1_1_1.jpg bg553colorSmallest_1_1.jpg
Figure 1: Crystal structure of 1 Figure 2: Crystal structure of 2

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Presentation: invited lecture at 18th Conference on Physical Organic Chemistry, Plenary session, by Daniel Kost
See On-line Journal of 18th Conference on Physical Organic Chemistry

Submitted: 2006-05-28 06:56
Revised:   2009-06-07 00:44