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

Reaction of SiX n Cl 4 - n (X = H, Me) with “Li(C(SiMe 3 ) 2 (2-C 5 H 4 N))” or “Li(C(SiMe 3 ) 2 (6-Me-2-C 5 H 3 N))” yields hypervalent five-coordinate compounds, established in the solid state for Si R HCl 2 ( 5 and 7 ), which show strong intramolecular Si−N interactions in the four-membered chelate ring (NSiC 2 ) that persist in solution (Si−N = 2.066(9) and 2.072(4) Å, X = H). Complexes based on HCPh 2 (2-C 5 H 4 N) form four-coordinate species, whereas complexes based on HCPh(SiMe 3 )(2-C 5 H 4 N) afford either four- or five-coordinate complexes; the rac isomers of Si(CH(SiMe 3 )(2-C 5 H 4 N)) 2 Me n Cl 2 - n ( 26 and 27 ), formed stereospecifically, are four-coordinate.