Organotin-Functionalized Crown Ethers as Ditopic Hosts for Lithium Salts: Synthesis, Structures and Complexation Studies of X3SnCH2[16]-crown-5 (X = I, Br, Cl)

The syntheses of the organotin-substituted crown ethers X3SnCH2[16]-crown-5 (2, X = I; 3, X = Br; 4, X = Cl), and the organostannate complex Ph4P[4<bold>Cl</bold>] are reported. These compounds are characterized by H-1, C-13, and Sn-119, NMR spectroscopy, elemental analyses, electrospray ionization mass spectrometry, and single-crystal X-ray diffraction studies. The solid-state structure of 2 is characterized by two intramolecular OSn interactions, whereas 3 and 4 each contain one intra- and one intermolecular OSn interactions involving crown ether and water oxygen atoms. The tin atoms are six-coordinate showing each a distorted octahedral environment. NMR spectroscopic studies indicate that hexacoordination is retained in solution. The compounds 3 and 4 are ditopic hosts for LiBr and LiCl, and have the ability to solubilize these salts in acetonitrile. The preferred selectivity of these compounds containing [16]-crown-5 moieties (known to be selective for sodium salts), towards lithium salts is credited to the increased Lewis acidity of the tin atom and hence the strong intramolecular OSn interactions.