Stereoselective Anion Template Effects: Syntheses and Molecular Structures of Tetraphenyl [12]Mercuracarborand-4 Complexes of Halide Ions

Zhiping Zheng, Carolyn B. Knobler, M. Frederick Hawthorne

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Abstract

The synthesis and characterization of the chloride and iodide ion complexes of a set of isomeric hydrophobic tetraphenyl [12]mercuracarborand-4 hosts having sterically encumbered cavities are described. These compounds [(3-C6H5-1,2-C2B10H9Hg)4] •XLi (3•XLi, X = Cl-and I-) were prepared by the reaction of the corresponding mercuric halides with cloao-3-Ph-1,2-Li2-1,2-C2B10H9. The presence of phenyl substituents in this system requires the existence of isomers in which the phenyl substituents are arrayed about the periphery of the host cavity. Three of four possible stereoisomers of the chloride ion complex were detected by HPLC analysis of the reaction mixtures, separated by recrystallization, identified as the desired species by the negative ion FAB mass spectrum, and structurally characterized by crystallography. X-ray diffraction data are as follows: 3a • ClLi (1,2-altemate structure with phenyl substituents in an “up”, “up”, “down”, “down” fashion): monoclinic, space group P2/a, a = 24.080(1) Å, b = 13.4509(8) Å, and c = 26.054(2) Å, β = 99.488(2)°, V = 8323 Å3, Z = 4, ϱc aled= 1.61 g cm-3, R = 0.056, Rw= 0.067. 3b• ClLi (1,3-altemate structure; phenyl substituents “up”, “down”, “up”, “down”): triclinic, space group P1, a = 12.8692(9) Å, b = 18.126(1) Å, and c = 18.309(1) Å, α = 114.593(2)°, β = 100.016(2)°, and γ = 97.259(2)°, V = 3729 Å3, Z = 2, R = 0.076, Rw= 0.097. 3c • ClLi (partial cone structure; phenyl substituents “up”, “up”, “up”, “down”): monoclinic, space group Cm, a = 16.405(2) Å, b = 18.928(3) Å, and c = 10.409(1) Å, β= 112.610(4)°, V = 2984 Å3, Z = 2, ϱcalcd= 1.91 g cm- 3, R = 0.032, Rw= 0.045. This molecule has a mirror plane. In contrast to these results, only one of four possible stereoisomers of the iodide ion complex was detected by HPLC analysis of the reaction mixtures. This species, 3b • ILi, was found to be a 1,3-altemate structure by X-ray analysis (phenyl substituents “up”, “down”, “up”, “down”) and was further characterized by multinuclear NMR and negative ion FAB mass spectroscopy. Crystal data: tetragonal, space group I41/amd, a = 17.520(2) Å, c = 35.432(5) Å, V = 10876 Å3, Z = 4, ϱcalcd= 1.23 g cm -3, R = 0.069, Rw= 0.095. Molecular modeling results preclude the formation of analogous 1,2-altemate or partial cone structures of the iodide ion complex. An acyclic host, 4, having two Lewis-acidic mercury atoms and three carborane units was prepared by reacting 3-Ph-1,2-Li2-1,2-C2B10H9with Hg(O2-CCH3)2- This species forms a 1:1 complex with ethanol in the solid state. Crystal data for 4 • (C2H5OH): monoclinic, space group P21/c, a = 14.542(4) Å, b = 17.861(5), c = 20.701(6) Å, β = 99.04(1)°, V = 5310 Å3, Z = 4, ϱcalcd= 1.21 g cm-3, R = 0.072, Rw= 0.083. The halide ion-specific kinetic template effects displayed by Cl-and I-ions during the stereoselective cyclization reaction are discussed.

Original languageEnglish (US)
Pages (from-to)5105-5113
Number of pages9
JournalJournal of the American Chemical Society
Volume117
Issue number18
DOIs
StatePublished - May 1995

ASJC Scopus subject areas

  • Catalysis
  • Chemistry(all)
  • Biochemistry
  • Colloid and Surface Chemistry

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