Monosaccharides as Silicon Chelators: Pentacoordinate Bis(diolato)(phenyl)silicates with the cis ‐Furanose Isomers of Common Pentoses and Hexoses

Five‐coordinate phenylsilicates are formed from the reaction of trimethoxy(phenyl)silane with monosaccharides in methanol in the presence of a stoichiometric amount of base. Five complexes have been isolated and characterized with two ketoses and three aldopentoses. The silicon central atom in [K([18]crown‐6)][PhSi(β‐ D ‐Fru f  2,3H −2 ) 2 ]⋅MeOH ( 1 , Fru=fructose) is part of two chelate rings, with the ligands being β‐ D ‐fructofuranose‐ O   2 , O   3 dianions. The β‐furanose isomer is best suited for silicon ligation because it exhibits a torsion angle close to 0° for the most acidic diol function, thus assuring a flat chelate ring. The same structural principles are also found in [K([18]crown‐6)][PhSi(β‐ D ‐Ara f 1,2H −2 ) 2 ]⋅2 MeOH ( 2 , Ara=arabinose), [K([18]crown‐6)][PhSi(α‐ D ‐Rib f 1,2H −2 ) 2 ] ( 3 , Rib=ribose), [K([18]crown‐6)][PhSi(α‐ D ‐Xyl f 1,2H −2 ) 2 ]⋅ acetone ( 4 , Xyl=xylose), and [K([18]crown‐6)][PhSi(α‐ D ‐Rul f 2,3H −2 ) 2 ] ( 5 , Rul=ribulose).