Studies on Long-Lived (Pentafluorosulfanyl)phenyl-Substituted Carbocations.

A variety of long-lived carbocations containing the p-(pentafluorosulfanyl)phenyl and m-(pentafluorosulfanyl)phenyl groups have been characterized by low-temperature NMR spectroscopy. In the case of potential nonclassical carbocations substituted with the p-(pentafluorosulfanyl)phenyl substituent, deviations from linearity when the Hammett parameter (σC+) is plotted versus 13C NMR shifts of the carbocationic center were observed. Plotting the experimentally derived 13C NMR shifts versus σC+ or σ+ of classical 4-phenyl-X substituted carbocations also provides a means to accurately back-calculate the σ+ and σC+ parameters of the -SF5 substituent.

The synthesis of organic carbonates from carbon dioxide.

Carbon dioxide (CO(2)) is an easily available, renewable carbon resource, which has the advantages of being non-toxic, abundant and economical. CO(2) is also attractive as an environmentally friendly chemical reagent, and is especially useful as a phosgene substitute. CO(2) is an "anhydrous carbonic acid" that rapidly reacts with basic compounds. Nucleophilic attack at CO(2) conveniently produces carboxyl and carbamoyl groups. Further reactions of these species with electrophiles lead to the formation of organic carbonates and carbamates. The present article deals with the synthetic technologies leading to organic carbonates using CO(2) as a raw material.

Fe(OTf)(3)-catalyzed addition of sp C-H bonds to olefins.

We have developed a novel acid-catalyzed addition of acetylenes to olefins in the presence of catalytic triflic acid or its metal salts. Among the various triflates, the catalytic activities depend on the cation and decrease in the order Fe(3+) > Al(3+) >> H(+), In(3+), Sc(3+) >> Cu(2+), Ag(+). In general, "hard" acids gave higher yields than "soft" acids such as copper and silver triflates. Among relatively hard acids, Fe(OTf)(3) was the best catalyst, which is also the case for ester formation from carboxylic acids and olefins. Our procedure is unique and attractive for the following reasons: (i) The reaction proceeds even for isolated C=C double bonds, as in norbornene. (ii) The reaction is promoted by acid catalysts and does not include an oxidation-reduction cycle for transition metals. (iii) Moreover, these catalysts are inexpensive, abundant, and less toxic than precious-metal-based catalysts. The reaction proceeds even under air and does not require precious metals.

Iron-catalysed green synthesis of carboxylic esters by the intermolecular addition of carboxylic acids to alkenes.

Iron triflate, in situ-formed from FeCl3 and triflic acid, or FeCl3 and silver triflate efficiently catalyse the intermolecular addition of carboxylic acids to various alkenes to yield carboxylic esters; the reaction is applicable to the synthesis of unstable esters, such as acrylates.

Potassium-selective membrane electrodes based on macrocyclic metacyclophanes analogous to calixarenes.

The tetrabutyl ester derived from 9,16,25,32-tetrahydroxy[3.1.3.1]metacyclophane was an excellent ionophore for constructing a K+-selective membrane electrode. This ionophore exhibited a much higher selectivity toward K+ than the structurally similar potassium ionophore IV commercially available from Fluka. In particular, the interference from organic ammonium ions decreased remarkably. Potassium ionophore IV possessed oxygen atoms in the ring structure, while the present ionophore changed the oxygen atoms to carbon atoms. Thus, the removal of oxygen atoms in ring constituents of the metacyclophane acted to reduce the interaction with the NH3+ group of organic ammonium ions. The size of the cavity of the present ionophore was between those of calix[4]arene and calix[6]arene derivatives, which act as Na+ and Cs+ ionophores, respectively, demonstrating that the ability to recognize alkali metal cations was strongly cavity size-dependent. The present K+-selective electrode had less interference from Rb+ and Cs+ than an electrode constructed using valinomycin, but suffered greater interference from Na+.