The ring-chain tautomeric equilibria of selenium macrocyclic compounds: the isolation of the ring tautomer.

A broadening of the investigation of the ring-chain tautomeric process of N-substituted 1,3-X,N-heterocycles (X = O, S, NR) to Se containing macrocyclic compounds allowed the isolation and structurally solid state characterization of the cyclic tautomer 7, which due to the length of the aliphatic chain, is able to form a stable six-membered ring (6-endo-trig). The theoretical calculations based on the DFT method (Gaussian 03 software package) also support the fact that tautomer 7 is more stable than the chain tautomer 6. Thus, based on the ring-chain tautomerism of the macrocycles that contain alkyl chains with amino-imino, imino-alcohol or sulphur-imino groups, combined with a strategy that allows the formation of a stable six-membered ring, the main reaction products will be the cyclic tautomers. The ring-chain equilibria of these macrocycles could be exploited advantageously in different areas of macrocyclic, physical and medicinal chemistry in order to obtain compounds with practical applications.

"Inverse sodium hydride": a crystalline salt that contains H(+) and Na(-).

A crystalline salt has been synthesized that contains H(+) and Na(-) rather than the usual hydride oxidation states of H(-) and Na(+). The key is irreversible encapsulation of H(+) within the cage of 3(6)adamanzane (Adz). The internal proton is kinetically inert to reduction by Na(-) in solution in NH(3)-MeNH(2) mixtures. Synthesis of the sodide is accomplished by a metathesis reaction between Na and AdzH(+)X(-) in which X(-) is a sacrificial anion such as glycolate, isethionate, or nitrate. Reduction or deprotonation of the sacrificial anion forms insoluble byproducts and AdzH(+)Na(-) in solution. After solvent removal, the sodide is dissolved in dimethyl ether and transferred through a frit into a separate chamber for crystallization. The compound was characterized as the sodide by analysis, NMR spectra, and optical absorption spectroscopy.

Supramolecular synthesis through dihydrogen bonds: self-assembly of controlled architectures from NaBH4 x poly(2-hydroxyethyl)cyclen building blocks.

A systematic investigation of molecular structures/supramolecular organization relationships in dihydrogen-bonded complexes comprising NaBH4 and poly-2-hydroxyethyl-cyclen (poly-HEC) building blocks is reported. Like in the prototype compound 1, a (NaBH4-poly-HEC)2 dimeric arrangement has been found in the analogous structures 3 and 5, but not in compound 2, which lacks dihydrogen bonds. The exact connectivity of the dimers is determined by a complex interplay of noncovalent interactions such as OH...HB dihydrogen bonds, OH...O conventional hydrogen bonds, Na-O and Na-N coordinative bonds, and dispersion interactions. The persistent recurrence of this general supramolecular motif permits controlled assembly of extended networks with desired architectures, by the use of appropriate spacers for linking the dimers, as demonstrated by the solid-state structure of 7. Additionally, the intrinsic solid-state reactivity of these dihydrogen-bonded networks makes this approach a promising strategy for the rational construction of functional extended covalent solids.