Alexander M. Genaev

Triarylmethanols with Bulky Aryl Groups and the NOESY/EXSY Experimental Observation of a Two-Ring-Flip Mechanism for the Helicity Reversal of Molecular Propellers

Triarylmethanols - the direct precursors of persistent trityl radicals - are racemic mixtures of chiral three-bladed molecular propellers. Depending on bulkiness of aryl groups they exhibit various liabilities to interconversion, the half- life time of room temperature racemization varying in a range between 8.4 hours and 1.32 years. NOESY/EXSY experiment performed on two representative models strongly supports the two-ring flip mechanism for the configurational interchange.

Protonation Behavior of 1,1′-Bi-2-naphthol and Insights into Its Acid-Catalyzed Atropisomerization

The behavior of 1,1-bi-2-naphthol (BINOL) in variety of (super)acid media has been studied by NMR. The results are combined with the theoretical (DFT) study of the role of mono- and diprotonated forms of BINOL in the acid-catalyzed atropisomerization of this compound. It is demonstrated that the process of enantiomeric configuration exchange proceeds mainly via internal rotation around the C1(sp3)-C1(sp3) bond in intermediates such as C1-monoprotonated keto or C1,C1-diprotonated forms of BINOL, depending on the acidity level.

Experimental and Theoretical Study of [2σ + 2σ + 2π]–Cycloaddition of Quadricyclane and Ethylenes Containing Three Silyl-Groups

The reaction of [2σ + 2σ + 2π]-cycloaddition of quadricyclane with olefins is an attractive way for regio- and sterospecific synthesis of norbornene derivatives (exo-tricyclononenes) with desired substituents. The presence of Cl3Si-containing groups in such compounds permits different monomer modifications for the development of new materials. Herein, for the first time the theoretical and experimental study of the behavior of different ethylenes containing three silyl-groups in the reaction of [2σ + 2σ + 2π]-cycloaddition with quadricyclane was systematically performed. Based on the data obtained for this reaction the activity scale of the ethylene derivatives was established, and the explanations for an ethylene activity were suggested. As a result, a new family of Si-containing tricyclononenes was successfully synthesized. As an example of a possible modification, the methylation of the sterically hindered cycloadducts was investigated and the conditions for full methylation were found. Considering that gas permeability of polymers increases with the increase of a number of the side Me3Si-groups, the compounds are interesting monomers for synthesis of membrane polymers possessing high gas permeability values.

Catalytic Asymmetric Addition of Diethylzinc to Benzaldehyde Using α- Pinene-Derived Ligands

The amines obtained from � -pinene and containing a phenol or pyridine fragment can be used as ligands in the asymmetric addition of diethylzinc to aromatic aldehydes; the enantiomeric excess (ee) was up to 80%. The enantioselectivity of the reaction is not very sensitive to the nature of substituents in the aromatic ring of aldehydes.

Noncatalytic bromination of benzene: A combined computational and experimental study

The noncatalytic bromination of benzene is shown experimentally to require high 5–14 M concentrations of bromine to proceed at ambient temperatures to form predominantly bromobenzene, along with detectable (<2%) amounts of addition products such as tetra and hexabromocyclohexanes. The kinetic order in bromine at these high concentrations is 4.8u2009±u20090.06 at 298 K and 5.6u2009±u20090.11 at 273 K with a small measured inverse deuterium isotope effect using D6‐benzene of 0.97u2009±u20090.03 at 298 K. These results are rationalized using computed transition states models at the B3LYP+D3/6‐311++G(2d,2p) level with an essential continuum solvent field for benzene applied. The model with the lowest predicted activation free energies agrees with the high experimental kinetic order in bromine and involves formation of an ionic, concerted, and asynchronous transition state with a Br8 cluster resembling the structure of the known Br9−. This cluster plays three roles; as a Br+ donor, as a proton base, and as a stabilizing arm forming weak interactions with two adjacent benzene Cuf8ffH hydrogens, these aspects together combining to overcome the lack of reactivity of benzene induced by its aromaticity. The computed inverse kinetic isotope effect of 0.95 agrees with experiment, and arises because Cuf8ffBr bond formation is essentially complete, whereas Cuf8ffH cleavage has not yet commenced. The computed free energy barriers for the reaction with 4Br2 and 5Br2 for a standard state of 14.3 M in bromine are reasonable for an ambient temperature reaction, unlike previously reported theoretical models involving only one or two bromines.

Formation of dications bearing a S(OH)2+ group from long-lived 9,9-dimethyl-10 R-phenanthrenium cations in FSO3H–SbF5/SO2ClF/SO2: a mechanistic study

1 n H and 13C NMR studies have shown that the long-lived 9,9-dimethyl-10-R-phenanthrenium cations (R = PhCC, Me, OH) generated in FSO3H–SbF5/SO2ClF/SO2/CD2Cl2 transform into long-lived 7-dihydroxysulfonio-9,9-dimethyl-10-R-phenanthrenium dications. The effect of the 10-R substituents on the reaction rate suggests that a key step in the reaction mechanism is addition of SO2 to protonated phenanthrenium cations.

Intramolecular borylation reaction catalyzed by Lewis acid: preparation of 1H-2,1-benzazaborole derivatives

It has been found that 1H-2,1-benzazaboroles can be nprepared by the interaction of substituted benzylaminochloroboranes with nAl2Cl6 in CH2Cl2 at 0 °C, nthe 13C NMR spectroscopy data obtained being in favour of an nelectrophilic substitution mechanism involving formation of cationic ncomplexes as reactive intermediates.

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.

Long-Lived Carbocations: Generation from 5,5,10,10-Tetramethyl-5,10-dihydroindeno[2,1-a]indene, Structure, and Rearrangements

According to the NMR data, protonation of 5,5,10,10-tetramethyl-5,10-dihydroindeno[2,1-a]indene in the system HSO3F-SO2ClF-CD2Cl2 at -80°C gives rise to long-lived 5,5,10,10-tetramethyl-2H-5,10-di- hydroindeno[2,1-a]indenium ion which undergoes isomerization into 4b,5,10,10-tetramethyl-4b,5,9b,10-tetra- hydroindeno[2,1-a]inden-5-yl cation on raising the temperature. On the basis of the data obtained for rear- rangements of such carbocations an alternative mechanism has been proposed for the rearrangements of struc- turally related carbocations having a bicyclo[3.3.0]octane skeleton.

FTIR spectra of matrix isolated 2-methylbenzonorbornen-2-yl-type cations

FTIR spectra suggest that ionization of n2-exo-chloro-2-methylbenzonorbornene nin an SbF5 matrix at -196 °C leads to n2-methyl-2-benzonortricyclyl cation which rearranges into a partially nπ-bridged 2-methylbenzonorbornen-2-yl ion at n-123 °C.