BIS-(2,3-NAPHTHALENEDIOLATO)-[2-(PYRROLIDINIO)ETHYL]SILICATE - SYNTHESIS AND STRUCTURAL CHARACTERIZATION OF A ZWITTERIONIC LAMBDA-5-SPIROSILICATE

The zwitterionic spirocyclic bis(2,3-naphthalenediolato)[2-(pyrrolidinio)ethyl]silicate [C-10H-6O2)2-SiCH2CH2(H)NC4H8, 3] was synthesized and its structure characterized (single crystal X-ray structural analysis; H-1, C-13 and Si-29 NMR studies of solutions in DMSO). 3 was obtained by reaction of cyclohexylmethoxyphenyl(2-pyrrolidinoethyl)silane [C6H11(CH3O)Si(C6H-5)CH2CH2NC4H8, 4] with 2,3-dihydroxynaphthalene [C-10H6(OH)2] in acetonitrile at room temperature (isolated as 3.CH3CN, yield 81%). The formation of 3 involves two unusual Si-C cleavage reactions (cleavage of Si-C6H-5 and Si-C6H11 under mild reaction conditions). In addition, 3 was prepared by reaction of 2,3-dihydroxynaphthalene with dimethoxyphenyl(2-pyrrolidinoethyl)silane [C6H-5(CH3O)2SiCH2CH2NC4H8, 5] and trimethoxy(2-pyrrolidinoethyl)silane [CH3O)3SiCH2CH2NC4H8, 6], respectively (isolated as 3.CH3CN; yields 83 and 86%, respectively). 3.CH3CN crystallizes in the space group Pbca with a = 8.877(2) angstrom, b = 22.823(4) angstrom, c = 24.597(4) angstrom, and Z = 8 (R = 0.0592, R(w) = 0.0592). The pentacoordinated Si atom of 3.CH3CN is surrounded by its ligands in a nearly ideal square-pyramidal fashion (four basal O atoms and one apical C atom). The CH3CN molecule does not coordinate to the Si atom.