Hypervalent Silicon via Intramolecular Coordination in a Four-Membered Ring in Complexes of Substituted Pyridyl Ligands

Reaction of SiXnCl4-n (X = H, Me) with "Li(C(SiMe3)(2)( 2-C5H4N))" or "Li(C(SiMe3)(2)(6-Me-2-C5H3N))" yields hypervalent five-coordinate compounds, established in the solid state for SiRHCl2 (5 and 7), which show strong intramolecular Si-N interactions in the four-membered chelate ring (NSiC2) that persist in solution (Si-N = 2.066(9) and 2.072(4) Angstrom, X = H). Complexes based on HCPh2(2-C5H4N) form four-coordinate species, whereas complexes based on HCPh(SiMe3)(2-C5H4N) afford either four- or five-coordinate complexes; the rac isomers of Si(CH(SiMe3)(2-C5H4N))(2)MenCl2-n (26 and 27), formed stereospecifically, are four-coordinate.