Construction of Inorganic Crown Ethers by s-Block-Metal-Templated Si-O Bond Activation

We herein report the synthesis, structures, coordination ability, and mechanism of formation of silicon analogs of crown ethers. An oligomerization of ² D₂ (I) (² D_n ,=(Me₄ Si₂ O)_n ) was achieved by the reaction with GaI₃ and MI_x (M=Li, Na, Mg, Ca, Sr). In these reactions the metal cations serve as template and the anions (I^- /[GaI₄ ]^- ) are required as nucleophiles. In case of MI_x =LiI, [Li(² D₃ )GaI₄ ] (1) is formed. In case of MI_x =NaI, MgI₂ , CaI₂ , and SrI₂ the compounds [M(² D₄ )(GaI₄ )_x ] (M=Mg²⁺ (3), Ca²⁺ (4), Sr²⁺ (5) are obtained. Furthermore the proton complex [H(² D₃ )][Ga₂ I₇ ] (6) was isolated and structurally characterized. All complexes were characterized by means of multinuclear NMR spectroscopy, DOSY experiments and, except for compound 3, also by single crystal X-ray diffraction. Quantum chemical calculations were carried out to compare the affinity of M⁺ to ² D_n and other ligands and to shed light on the formation of larger rings from smaller ones.