G. E. Sal'nikov

Nature of Bonding in Donor–Acceptor Interactions Exemplified by Complexes of N‐Heterocyclic Carbenes with 1,2,5‐Telluradiazoles

Comprehensive structural, spectroscopic, and quantum chemical analyses of new donor-acceptor complexes between N-heterocyclic carbenes and 1,2,5-telluradiazoles and a comparison with previously known complexes involving tellurenyl cations showed that the dative C-Te bonds cannot be solitarily described with only one Lewis formula. Canonical Lewis formulas that denote covalency and arrows emphasizing ionicity complement each other in varying extents. Evaluation of the relative weights of these resonance forms requires proper bonding description with a well-balanced toolbox of analytical methods. If for conciseness only, one resonance form is used, it must be the most significant one according to the analytical evaluation. If unclear, all significant resonance forms should be displayed.

Derivatives of L-Pimaric Acid in the Synthesis of Chiral Organophosphorus Ligands from Decahydrophenanthrene Series

Starting with maleopimaric and fumaropimaric acids were prepared chiral organophosphorus ligands from decahydrophenanthrene series. Cationic complexes of Rh(I) prepared therefrom were tested for catalysts of asymmetric hydrogenation of unsaturated precursors of N-acethylphenylalanine and its derivatives.

Fused 1,2,3-Thiaselenazoles Synthesized from 1,2,3-Dithiazoles through Selective Chalcogen Exchange

A new approach to the synthesis of fused 1,2,3-thiaselenazoles-rare five-membered heterocycles that contain two different chalcogens-from the corresponding 1,2,3-dithiazoles and SeO2 was accomplished by selective exchange of S and Se atoms. The fused carbo- and heterocyclic units were indene, naphthalenone, cyclohexadienone, cyclopentadiene, benzoannulene, and benzoxazine. The molecular structures of two of the thiaselenadiazole products and one of the dithiazole precursors were confirmed by single-crystal X-ray diffraction. The reaction is highly solvent selective; it only takes place in solvents that contain a C=O group (e.g., DMF or tetramethylurea). According to DFT calculations, the reaction is thermodynamically favorable. Based on the DFT calculations and 77 Se NMR spectroscopy, two tentative mechanisms that feature isomeric transition states and intermediates are suggested for the reaction via ring-opening addition of SeO2 to the S-X dithiazole bond (X=N or S). The DFT-calculated first adiabatic electron affinities of the compounds were chalcogen independent and positive in all cases, which assumes formation of thermodynamically stable radical anions (RAs). These calculated RAs featured either normal or abnormal elongation of the S1-X2 (X=S or Se) bond relative to their neutral precursors and possessed π* or σ* SOMOs, respectively.

Polyfunctional triterpenoids from the bark of Yeddo spruce

The composition of the polyfunctional triterpenoids of an extract of the Yeddo spruce has been studied. Five serratene triterpenoids have been isolated: 21β-hydroxyserrat-14-en-3-one (I), 3β-hydroxyserrat-14-en-21-one (II), serratenediol (III), episerratenediol (XII), and diepiserratenediol (V) in the form of its acetate. The structures of the compounds were confirmed by13C NMR spectra and XSA.

Configurational Stability of 1,1′-Bi-2-naphthol in Superacid System HSO 3 F–SbF 5 –SO 2 ClF

Although 1,1′-bi-2-naphthol (BINOL) is known to racemize in aqueous mineral acids and much more readily in superacids, it retains its initial configuration in one of the strongest superacid system, HSO3F-SbF5-SO2ClF due to protective C8,C8′-diprotonation.

Donor-Acceptor Complexes between 1,2,5-Chalcogenadiazoles (Te, Se, S) and the Pseudohalides CN− and XCN− (X=O, S, Se, Te)

Donor-acceptor (D-A) complexes between 3,4-dicyano-1,2,5-chalcogenadiazoles [chalcogen=Te (1 a), Se (1 b), S (1 c)] and the pseudohalides CN- and XCN- (X=O, S, Se, Te) were studied experimentally and theoretically. For 1 a, they were isolated as [K(18-crown-6)][1 a-CN] (2), [K(18-crown-6)][1 a-NCO] (3), [K(18-crown-6)][1 a-SCN] (4), [K(18-crown-6)][1 a-SeCN] (5), and [K][1 a-NCSe] (6) and characterized by X-ray diffraction (XRD), UV/Vis and NMR spectroscopy, and DFT and QTAIM calculations. For 1 b and 1 c, the complexes were not isolated due to unfavorable thermodynamics. In all isolated complexes, the D-A bonds, stabilized by negative hyperconjugation, were longer than the sum of the covalent radii and shorter than the sum of the van der Waals radii of the bonded atoms. In mixtures of 1 a, F- , and SeCN- , the complex [1 a-F]- was selectively formed in accordance with thermodynamics. The reaction of 1 a with SeCN- and the cyclic trimeric perfluoro-ortho-phenylene mercury afforded the complex [K(18-crown-6)][SCN]⋅(o-C6 F4 Hg)3 , which was characterized by XRD.

Radical Anions, Radical-Anion Salts and Anionic Complexes of 2,1,3-Benzochalcogenadiazoles (S, Se, Te)

By means of cyclic voltammetry (CV) and DFT calculations, it was found that the electron-acceptor ability of 2,1,3-benzochalcogenadiazoles 1-3 (chalcogen: S, Se, and Te, respectively) increases with increasing atomic number of the chalcogen. This trend is nontrivial, since it contradicts the electronegativity and atomic electron affinity of the chalcogens. In contrast to radical anions (RAs) [1].- and [2].- , RA [3].- was not detected by EPR spectroscopy under CV conditions. Chemical reduction of 1-3 was performed and new thermally stable RA salts [K(THF)]+ [2].- (8) and [K(18-crown-6)]+ [2].- (9) were isolated in addition to known salt [K(THF)]+ [1].- (7). On contact with air, RAs [1].- and [2].- underwent fast decomposition in solution with the formation of anions [ECN]- , which were isolated in the form of salts [K(18-crown-6)]+ [ECN]- (10, E=S; 11, E=Se). In the case of 3, RA [3].- was detected by EPR spectroscopy as the first representative of tellurium-nitrogen π-heterocyclic RAs but not isolated. Instead, salt [K(18-crown-6)]+ 2 [3-Te2 ]2- (12) featuring a new anionic complex with coordinate Te-Te bond was obtained. On contact with air, salt 12 transformed into salt [K(18-crown-6)]+ 2 [3-Te4 -3]2- (13) containing an anionic complex with two coordinate Te-Te bonds. The structures of 8-13 were confirmed by XRD, and the nature of the Te-Te coordinate bond in [3-Te2 ]2- and [3-Te4 -3]2- was studied by DFT calculations and QTAIM analysis.

Formation of 3-Methyl-1-adamantyl Trifluoromethanesulfonate in the Reaction of 3,7-Dimethylenebicyclo[3.3.1]nonane with Trifluoromethanesulfonic Acid. Dissociation and Carbocationic Rearrangements

According to the 1H NMR data, the reaction of equimolar amounts of 3,7-dimethylenebicyclo[3.3.1]nonane with trifluoromethanesulfonic acid in CD2Cl2 leads to formation of 3-methyl-1-adamantyl trifluoromethanesulfonate. Further addition of trifluoromethanesulfonic acid promotes partial dissociation of 3-methyl-1-adamantyl trifluoromethanesulfonate into 3-methyladamantyl cation and trifluoromethanesulfonate anion, and the cation undergoes fast pericyclic rearrangement involving migration of bridgehead hydrogen atoms to the cationic center.