Competing ferro- and antiferromagnetic interactions in (manganese,sodium)phenylsilsesquioxane with metal oxide fragments

Magnetic measurements of individual (manganese,sodium)phenylsilsesquioxane containing eight Mn^II ions were performed. The magnetic arrangement of manganese ions in this cage-like compound was investigated. The magnetic moment of the cage molecule equals 21 μ_B (at 300 K), that is a consequence of the mutual antiferromagnetic compensation of four Mn^II ions, whereas the other four Mn^II ions have aligned spins. Hence, this metallasiloxane is a promising compound for the chemical design of molecular nanomagnets. At low temperatures, the antiferromagnetic coupling causes a decrease in the effective magnetic moment (to 16 μ_B at 40 K).     

5alpha-Ergost-24(28)-ene-3,6-dione - new steroid from the Pacific sponge Geodinella robusta

A new diketosteroid, 5alpha-ergost-24(28)-ene-3,6-dione (1), has been isolated from the sponge Geodinella robusta. Its structure was determined by combined spectroscopic methods and chemical evidence.     

Non-covalent interactions in stoichiometric and catalytic reactions of iridium pincer complexes

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Iridium and rhodium complexes with the planar chiral thioether ligands in asymmetric hydrogenation of ketones and imines

Rhodium complexes with the planar chiral phosphinoferrocenyl thioether ligands [Rh(P,SR)(diene)X] (R = Me, Bu^t, Ph, Bn, diene is cyclooctadiene (COD) or norbornadiene (NBD), X = Cl, BF₄) catalyze hydrogenation of ketones, imines, and heteroaromatic compounds; in the case of acetophenone, the enantioselectivity reached 60% ee. Similar iridium complexes demonstrate a good activity in the hydrogenation of imines, the maximal enantioselectivity in the case of N-phenyl-N-(1-phenylethylidene)amine was about 40% ee.     

N-Phenacylpyridinium Bromides as Acid Corrosion Inhibitors

The inhibiting effect of N-phenacylpyridinium bromides with the amide group in the pyridine ring on corrosion of carbon steel in 3 M sulfuric acid is studied. A relationship between the nature of substituents at the amide group and the corrosion-protective properties of the compounds studied is revealed. Compounds demonstrating high protection efficiency in acid solutions at elevated temperatures are found.     

Principle and mechanism of direct porphyrin metalation: joint experimental and theoretical investigation

The direct metalation of tetraphenylporphyrin with bare metal atoms (Co and Zn) was studied with X-ray photoelectron spectroscopy, scanning tunneling microscopy, and temperature-programmed reaction measurements on ordered monolayer films of the molecules adsorbed on a Ag(111) surface. The mechanism of this novel type of surface reaction was investigated using density functional theory (DFT) calculations for the related gas-phase reactions of the unsubstituted porphyrin with the metals Fe, Co, Ni, Cu, and Zn. The reaction starts with the formation of an initial complex, in which the metal atom is coordinated by the intact unreduced porphyrin. This complex resembles the sitting-atop complex proposed for porphyrin metalation with metal ions in solution. In two subsequent steps, the pyrrolic hydrogen atoms are transferred to the metal atom, forming H2, which is eventually released. The activation barriers of the H-transfer steps vary for the different metal atoms. DFT calculations suggest that metalations with Fe, Co, and Ni show two-state reactivity, while those with Cu and Zn proceed on a single potential energy surface. For metalation with Zn, we calculated a barrier of the first hydrogen transfer step of 32.6 kcal mol(-1), in good agreement with the overall experimental activation energy of 31 kcal mol(-1).     

Synthesis of new derivatives of D 3-trishomocubane

Russian Journal of Organic Chemistry -