Pentacoordinate Silyl Cations Stabilized by Coordination with Oxygen Donors: Crystal Structure, Charge Distribution, and Stereodynamics

Attempted preparation of neutral hexacoordinate silicon chelates with two O→Si dative bonds ( 4 ), in analogy to previously reported bis-N→Si isomers ( 2 ), resulted in unexpected formation of pentacoordinate siliconium complexes ( 5 and 6 ), characterized by a crystal structure. The barrier for inversion of configuration at silicon was determined by selective inversion recovery NMR measurements: Δ G * = 20.5 ± 0.2 kcal mol -1 .