[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 <i>Si</i>O<sub>3</sub>C<sub>2</sub> skeleton was synthesized, [benzene-1,2-diolato(2−)][benzene-1,2-diolato(1−)]methyl[(2,2,6,6-tetramethylpiperidinio)methyl]silicate (<b>11</b>). 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 <b>11</b> was obtained by treatment of dimethoxy(methyl)[(2,2,6,6-tetramethylpiperidino)methyl]silane (<b>10</b>) with 2 molar equiv of 1,2-dihydroxybenzene and was structurally characterized in solution (<sup>1</sup>H, <sup>13</sup>C, and <sup>29</sup>Si NMR) and in the solid state (<sup>29</sup>Si VACP/MAS NMR; crystal structure analysis of the solvate <b>11</b>·2CH<sub>2</sub>Cl<sub>2</sub>). Upon heating in acetonitrile, <b>11</b> 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 (<b>12</b>). The reaction sequence <b>10</b> → <b>11</b> (isolated intermediate) → <b>12</b> 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.