Hydride shift from silicon to an adjacent imino carbon ("intramolecular hydrosilylation") is observed in the reaction of MeSiHCl 2 with O-trimethylsilyl-N-(alkylidenimino)imidates [RC(OSiMe 3 )dNNdCR 1 R 2 ; R ) Me, Ph, CH 2 Ph, t-Bu; R 1 , R 2 ) Me ( 1), (CH 2 ) n (9), Ph, H ( 14)], leading to pentacoordinate silicon complexes. The reaction proceeds further to rearrange to the tricyclic pentacoordinate complexes, observed previously as products of intramolecular aldol condensation of imine moieties residing on two chelate rings in the reactions of XSiCl 3 (X ) alkyl, aryl) and 1.

Hexacoordinate silicon dichelates with hydrido and methyl monodentate ligands were prepared by transsilylation. The temperature-dependent 29 Si NMR spectra of toluene-d 8 or CDCl 3 solutions provide evidence for a reversible, neutral dissociation of the dative N-Si bond, accompanied by a shift of the 29 Si resonance from high field (hexacoordinate) to lower field (pentacoordinate) with increasing temperature. When a phenyl group is attached directly to silicon (replacing methyl), the N-Si dissociation is prevented, presumably due to electron withdrawal by the phenyl. Two of the silicon complexes were characterized by crystallographic analysis. Quantum chemical calculations at the RB3LYP/6-31G(d) level confirm the stability of an N-Si dissociated species (1.03 kcal mol -1 lower in energy than the hexacoordinate dichelate) and rule out the alternative possibility of an O-Si zwitterionic dissociation, thus supporting the mechanism suggested by the experimental results.

The synthesis and properties of dinuclear silicon complexes derived from uracil, barbituric acid, and 5,5-dimethylbarbituric acid, through the reaction with (chloromethyl)dimethylchlorosilane and (chloromethyl)dichloro(methyl)silane are described. The oxygen atoms are weakly coordinated to silicon in all three groups of compounds. Mild hydrolysis of the dinuclear compounds leads to formation of cyclic oligomers, with 2-9 monomer units in each, in which the individual units are connected through siloxane groups. Lithium chloride is shown to act as an effective template, restricting oligomerization to dimers and preventing higher-mass product formation.

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