Supramolecular complexes of La@C82 with unsaturated thiacrown ethers.

The paramagnetic La@C82-A(C2v) with unsaturated thiacrown ethers forms 1 : 1 host-guest complexes of [La@C82-A(C2v)]-[D]+ in solution as a result of electron transfer.

Optical resolution and racemization mechanism of a tellurinic acid.

[reaction: see text] Optically active tellurinic acid was obtained for the first time by chromatographic resolution of racemic 2,4,6-triisopropylbenzenetellurinic acid (1) using a chiral column. Optically active tellurinic acid (+)-1 was stable toward racemization in hexane, although racemization occurred in hexane/2-propanol. The kinetic studies for the racemization, oxygen exchange reaction using H(2)(18)O, and theoretical studies clarified that the racemization of the optically active tellurinic acid in solution proceeds via a hypervalent tellurane formed by addition of water remaining in solvent.

Synthesis and structures of 15- and 18-membered unsaturated selenacrown ethers and their complexation with silver trifluoroacetate.

The reaction of Na(2)Se with cis-dichloroethene yielded (Z,Z,Z,Z,Z)-1,4,7,10,13-pentaselenacyclopentadeca-2,5,8,11,14-pentaene (15-US-5) and (Z,Z,Z,Z,Z,Z)-1,4,7,10,13,16-hexaselenacyclooctadeca-2,5,8,11,14,17-hexaene (18-US-6). X-ray crystallographic analysis of 15-US-5 and 18-US-6 revealed an all-cis geometry around the carbon-carbon double bonds, with all of the selenium atoms located on one side of the respective ring planes. 15-US-5 and 18-US-6 were also found to be oxidized more easily than the corresponding sulfur analogues. The complexation of 15-US-5 and 18-US-6 with silver trifluoroacetate afforded Ag(I)(15-US-5)(CF(3)COO) and Ag(I)(5)(18-US-6)(3)(CF(3)COO)(5), respectively. [reaction: see text]

Syntheses and Peculiar Behavior in Solutions of Optically Active Telluronium Salts.

A diastereomeric (epimeric) mixture of ethylmethylphenyltelluronium (1S)-(+)-camphor-10-sulfonate (dia.-1) was optically resolved by fractional recrystallization into the diastereomerically pure isomers (R)(Te)-1 and (S)(Te)-1. The absolute configurations of the isomers were determined by the X-ray crystallographic analysis of (R)(Te)-1. Enantiomerically pure (R)-ethylmethylphenyltelluronium perchlorate, tetrafluoroborate, p-chlorobenzenesulfonate, bornane-10-sulfonate, tetraphenylborate, and picrylsulfonate (R)-2-7 were isolated, respectively, by anion-exchange reactions of diastereomerically pure (R)(Te)-1. The optically active telluronium salts were found to show peculiar optical properties on their specific rotations and circular dichroism spectra in solutions compared with those of the corresponding sulfonium and selenonium salts. On the basis of NMR studies, the behavior on the optical properties of the optically active telluronium salts was found to be caused by a strong solvation in polar solvents.

Optical Resolution and Configurational Stability of Selenoxides Stabilized by Intramolecular Coordination.

2-((Dimethylamino)methyl)phenyl alkyl (or aryl) selenoxides, configurationally stabilized by intramolecular coordination of an amino group to the selenium atom, were optically resolved into their enantiomeric isomers by means of high-performance liquid chromatography using an optically active column packed with amylosecarbamate derivative/silica gel. This is the first example of the isolation of optically pure selenoxides without bulky substituents and also the first isolation of optically pure alkyl aryl selenoxides. The absolute configuration of the (-)-isomers could be assigned to be the S-form by comparison of their specific rotations, circular dichroism spectra, and behavior on the optically active column with those of the sulfur analogue, prepared by Andersen's method. Racemization of the optically active selenoxides was accelerated not only in acidic solution but also in basic media. This result indicates there are two different mechanisms for their racemization in acidic and basic media. The stabilization energy of the selenoxides by the intramolecular coordination of an amino group to the selenium atom was estimated to be ca. 3 kcal mol(-)(1) on the basis of variable-temperature (1)H NMR measurements.

Molecular transformations of unsaturated thiacrown ethers.

Unsaturated thiacrown ethers with 15, 18, and 21 members were oxidized to sulfoxides by the reaction with m-CPBA. The reaction with t-BuOCl at -20 degrees C also afforded sulfoxides, whereas the reaction at room temperature yielded cis-trans isomerized compounds. The cis-trans isomerized compound was also obtained by the photochemical reaction or by the reaction with NCS and NCP. Meanwhile, the reaction with NBS and NBP provided an acetal via 1,2-bridged bromonium intermediate.

Optically active seleninamides: isolation, absolute configuration, and racemization mechanism.

Optically active seleninamides were obtained for the first time by chromatographic resolution on an optically active column. The absolute configurations of the optically active seleninamides were determined by comparing their chiroptical properties with those of analogous sulfinamides, the stereochemistry of which was determined by transformation into chiral sulfoxides of known configurations. The optically active seleninamides were found to racemize in solution. Kinetic studies of the racemization and theoretical studies clarified that the racemization of the optically active seleninamides in solution proceeds via hypervalent hydrates formed by the reaction with water.

Optically active seleninate esters: isolation, absolute configuration, racemization mechanism, and transformation into chiral selenoxide.

Optically active seleninate esters were obtained for the first time by chromatographic resolution on an optically active column. The absolute configurations of the optically active seleninate esters were determined by comparing their chiroptical properties with those of two analogous sulfinate esters, the absolute configuration of one of which is known and that of the other was determined by X-ray crystallographic analysis. The optically active seleninate esters were found to racemize in solution. Kinetic studies of the racemization, the oxygen exchange reaction with H(2)(18)O, and theoretical studies clarified that the racemization of the optically active seleninate esters in solution proceeded via an achiral hypervalent selenurane intermediate that was formed by the reaction with water. The reaction of the optically active seleninate ester and the sulfinate ester having bulky substituents with Grignard reagents was found to proceed with the retention of stereochemistry to give an optically active selenoxide and sulfoxides, respectively.

Unsaturated selenacrown ethers: synthesis, structure, and formation of silver complexes.

The unsaturated selenacrown ethers, (Z,Z,Z,Z,Z)-1,4,7,10,13-pentaselenacyclopentadeca-2,5,8,11,14-pentaene (15-US-5) (2), (Z,Z,Z,Z,Z,Z)-1,4,7,10,13,16-hexaselenacyclooctadeca-2,5,8,11,14,17-hexaene (18-US-6) (3), (Z,Z,Z,Z,Z,Z,Z)-1,4,7,10,13,16,19-heptaselenacycloheneicosa-2,5,8,11,14,17,20-heptaene (21-US-7) (4), (Z,Z,Z,Z,Z,Z,Z,Z)-1,4,7,10,13,16,19,22-octaselenacyclotetracosa-2,5,8,11,14,17,20,23-octaene (24-US-8) (5), and (Z,Z,Z,Z,Z,Z,Z,Z,Z)-1,4,7,10,13,16,19,22,25-nonaselenacycloheptacosa-2,5,8,11,14,17,20,23,26-nonaene (27-US-9) (6), were obtained together with 1,4-diselenin (1) by reacting sodium selenide with cis-dichloroethene in the presence of a phase-transfer catalyst. The crystal structures of 2-5 were determined by X-ray crystallographic analysis. The UV spectra of the selenacrown ethers showed absorption maximums in the range of 251-262 nm, which were assigned to n-->pi transitions. The cyclic voltammograms indicated that the large unsaturated selenacrown ethers were oxidized more easily than the small ones. The thermal reactions of the unsaturated selenacrown ethers afforded 1,4-diselenin (1) along with polymeric materials, whereas 1 was thermally stable even at 100 degrees C. The reactions of 1 or unsaturated selenacrown ethers 2-5 with silver ion yielded various novel silver complexes, Ag(C(4)H(4)Se(2))(CF(3)COO) (7), Ag(C(4)H(4)Se(2))(2)(CF(3)COO) (8), Ag(15-US-5)(CF(3)COO) (9), Ag(5)(18-US-6)(3)(CF(3)COO)(5) (10), Ag(7)(21-US-7)(CF(3)COO)(5) (11), Ag(24-US-8)(2)(CF(3)COO) (12), Ag(2)(24-US-8)(CF(3)COO)(2) (13), Ag(3)(24-US-8)(2)(CF(3)COO)(3) (14), Ag(15-US-5)NO(3) (15), and Ag(21-US-7)BF(4) (16). The stoichiometry for the complexation with silver trifluoroacetate in solution was examined by (1)H NMR measurement. The titration plots of 2 and 5 under the dilution conditions showed a distinct inflection point at the 1/1 metal/macrocycle ratio, whereas the plots of 1 and 3 showed gradual change.

Formation and structures of mercury complexes of 18-membered unsaturated and saturated thiacrown ethers.

The complexation of 18-membered unsaturated thiacrown ether, 18-UT-6, with 1 equiv of HgCl(2) in acetone afforded mercury complex Hg(II)(18-UT-6)Cl(2). The complexations of 18-membered saturated thiacrown ether, 18S6, with 1 equiv each of HgCl(2) and CdCl(2) in acetone afforded Hg(II)(18S6)Cl(2) and Cd(II)(18S6)Cl(2), respectively. The crystal structure of Hg(II)(18-UT-6)Cl(2) revealed that the mercury atom was inside the cavity of the macrocycle and the geometry around the mercury atom was an eight-coordinate hexagonal bipyramidal arrangement. ORTEP drawing of Hg(II)(18S6)Cl(2) revealed the existence of the mercury atom outside the cavity of the ring, as well as a polymeric chain structure. (1)H NMR study of Hg(II)(18-UT-6)Cl(2) in acetone-d(6) indicated that the interconversion between free 18-UT-6 and pure complex was slower than the NMR time scale. The titration experiment by (1)H NMR revealed that 18-UT-6 had inclusion selectivity for the number of mercury atoms. The electrochemical behavior of complexes Hg(II)(18-UT-6)Cl(2) and Hg(II)(18S6)Cl(2) was also examined.

Silver complexes with unsaturated thiacrown ethers: inclusion behavior of conformationally restricted macrocycles.

The reactions of 18- and 21-membered unsaturated thiacrown ethers, 18-UT-6 and 21-UT-7, with CF(3)COOAg in acetone afforded novel silver(I) complexes Ag(I)(18-UT-6)(CF(3)COO) and Ag(I)(2)(21-UT-7)(CF(3)COO)(2), respectively. The crystal structure of Ag(I)(18-UT-6)(CF(3)COO) shows that the silver atom occupies the cavity of the 18-UT-6 and the geometry around the silver atom has a distorted five-coordinate square pyramidal arrangement. The crystal structure of Ag(I)(2)(21-UT-7)(CF(3)COO)(2) shows that the two silver atoms and all sulfur atoms are nearly coplanar and the two trifluoroacetate groups are located at the opposite sides of the plane. The stoichiometry for the complexation of 15-UT-5, 18-UT-6, and 21-UT-7 with CF(3)COOAg in solution was examined by (1)H NMR measurement. The titration plots of 15-UT-5 and 21-UT-7 show a distinct inflection point at 1:1 and 2:1 metal/macrocycle ratios, respectively, whereas the plot of 18-UT-6 gradually changes at the range of 1:1 to 2:1. From these results, 15-UT-5 and 21-UT-7 were found to show inclusion selectivity for number of silver ions, respectively, whereas 18-UT-6 showed low selectivity for the inclusion number of metals. Comparison of the oxidation and reduction potentials of the silver(I) complexes with those of free macrocycles and CF(3)COOAg revealed that unsaturated thiacrown ethers become difficult to be oxidized by complexation with CF(3)COOAg, and CF(3)COOAg becomes difficult to be reduced by complexation with unsaturated thiacrown ethers.