[Benzene-1,2-diolato(2−)][benzene-1,2-diolato(1−)]methyl[(2,2,6,6-tetramethylpiperidinio)methyl]silicate:  Isolation, Structural Characterization, and Thermally Induced Methane Elimination

A novel zwitterionic pentacoordinate silicon(IV) complex with an SiO₃C₂ skeleton was synthesized, [benzene-1,2-diolato(2−)][benzene-1,2-diolato(1−)]methyl[(2,2,6,6-tetramethylpiperidinio)methyl]silicate (11). It contains one bidentate benzene-1,2-diolato(2−) ligand and one monodentate benzene-1,2-diolato(1−) ligand, a new structural motive in silicon(IV) coordination chemistry. Compound 11 was obtained by treatment of dimethoxy(methyl)[(2,2,6,6-tetramethylpiperidino)methyl]silane (10) with 2 molar equiv of 1,2-dihydroxybenzene and was structurally characterized in solution (¹H, ¹³C, and ²⁹Si NMR) and in the solid state (²⁹Si VACP/MAS NMR; crystal structure analysis of the solvate 11·2CH₂Cl₂). Upon heating in acetonitrile, 11 undergoes a methane elimination to afford the zwitterionic spirocyclic pentacoordinate silicon(IV) complex bis[benzene-1,2-diolato(2−)][(2,2,6,6-tetramethylpiperidinio)methyl]silicate (12). The reaction sequence 10 → 11 (isolated intermediate) → 12 gives some insight into the mechanism of the reaction of dialkoxy(aminoorganyl)organylsilanes with organic diols to yield zwitterionic pentacoordinate silicon(IV) complexes of the (ammonioorganyl)bis[diolato(2−)]silicate type.