282 research outputs found
Політичні процеси в українському суспільстві на початку ХХІ століття
У статті висвітлюються питання щодо наукового осмислення
політичних процесів розвитку українського суспільства на
початку ХХІ століття та ролі політичної науки у процесах його
функціонування.The author reviews the problems of scientific conceptualizing of
political processes of the development of Ukrainian society at the
beginning of the 21-st century and the role of political science in
processes of its functioning
Scope and Mechanistic Study of the Coupling Reaction of α,β-Unsaturated Carbonyl Compounds with Alkenes: Uncovering Electronic Effects on Alkene Insertion vs Oxidative Coupling Pathways
The cationic ruthenium-hydride complex [(C6H6)(PCy3)(CO)RuH]+BF4– (1) was found to be a highly effective catalyst for the intermolecular conjugate addition of simple alkenes to α,β-unsaturated carbonyl compounds to give (Z)-selective tetrasubstituted olefin products. The analogous coupling reaction of cinnamides with electron-deficient olefins led to the oxidative coupling of two olefinic C–H bonds in forming (E)-selective diene products. The intramolecular version of the coupling reaction efficiently produced indene and bicyclic fulvene derivatives. The empirical rate law for the coupling reaction of ethyl cinnamate with propene was determined as follows: rate = k[1]1[propene]0[cinnamate]−1. A negligible deuterium kinetic isotope effect (kH/kD = 1.1 ± 0.1) was measured from both (E)-C6H5CH═C(CH3)CONHCH3 and (E)-C6H5CD═C(CH3)CONHCH3 with styrene. In contrast, a significant normal isotope effect (kH/kD = 1.7 ± 0.1) was observed from the reaction of (E)-C6H5CH═C(CH3)CONHCH3 with styrene and styrene-d8. A pronounced carbon isotope effect was measured from the coupling reaction of (E)-C6H5CH═CHCO2Et with propene (13C(recovered)/13C(virgin) at Cβ = 1.019(6)), while a negligible carbon isotope effect (13C(recovered)/13C(virgin) at Cβ = 0.999(4)) was obtained from the reaction of (E)-C6H5CH═C(CH3)CONHCH3 with styrene. Hammett plots from the correlation of para-substituted p-X-C6H4CH═CHCO2Et (X = OCH3, CH3, H, F, Cl, CO2Me, CF3) with propene and from the treatment of (E)-C6H5CH═CHCO2Et with a series of para-substituted styrenes p-Y-C6H4CH═CH2 (Y = OCH3, CH3, H, F, Cl, CF3) gave the positive slopes for both cases (ρ = +1.1 ± 0.1 and +1.5 ± 0.1, respectively). Eyring analysis of the coupling reaction led to the thermodynamic parameters, ΔH⧧ = 20 ± 2 kcal mol–1 and ΔS⧧ = −42 ± 5 eu. Two separate mechanistic pathways for the coupling reaction have been proposed on the basis of these kinetic and spectroscopic studies
ŽELJKO HOLJEVAC GOSPIĆ U VOJNOJ KRAJINI
A range of novel heterocyclic cations
have been synthesized by
the Rh(III)-catalyzed oxidative C–N and C–C coupling
of 1-phenylpyrazole, 2-phenylpyridine, and 2-vinylpyridine with alkynes
(4-octyne and diphenylacetylene). The reactions proceed via initial
C–H activation, alkyne insertion, and reductive coupling, and
all three of these steps are sensitive to the substrates involved
and the reaction conditions. Density functional theory (DFT) calculations
show that C–H activation can proceed via a heteroatom-directed
process that involves displacement of acetate by the neutral substrate
to form charged intermediates. This step (which leads to cationic
C–N coupled products) is therefore favored by more polar solvents.
An alternative non-directed C–H activation is also possible
that does not involve acetate displacement and so becomes favored
in low polarity solvents, leading to C–C coupled products.
Alkyne insertion is generally more favorable for diphenylacetylene
over 4-octyne, but the reverse is true of the reductive coupling step.
The diphenylacetylene moiety can also stabilize unsaturated seven-membered
rhodacycle intermediates through extra interaction with one of the
Ph substituents. With 1-phenylpyrazole this effect is sufficient to
suppress the final C–N reductive coupling. A comparison of
a series of seven-membered rhodacycles indicates the barrier to coupling
is highly sensitive to the two groups involved and follows the trend
C–N<sup>+</sup> > C–N > C–C (i.e., involving
the formation of cationic C–N, neutral C–N, and neutral
C–C coupled products, respectively)
Rhodium(III)-Catalyzed Dearomatizing (3+2) Annulation of 2-Alkenylphenols and Alkynes
Appropriately substituted 2-alkenylphenols undergo a mild formal [3C+2C] cycloaddition with alkynes when treated with a Rh(III) catalyst and an oxidant. The reaction, which involves the cleavage of the terminal C–H bond of the alkenyl moiety and the dearomatization of the phenol ring, provides a versatile and efficient approach to highly appealing spirocyclic skeletons and occurs with high selectivityWe thank the financial support provided by the Spanish Grants SAF2010-20822-C02 and CSD2007-00006 Consolider Ingenio 2010, the Xunta de Galicia Grants GR2013-041 and EM2013/036, the ERDF, and the European Research Council (Advanced Grant No. 340055). M.G. thanks Xunta de Galicia for a Parga Pondal contractS
Modular design of SPIRO-OMeTAD analogues as hole transport materials in solar cells
We predict the ionisation potentials of the hole-conducting material SPIRO-OMeTAD and twelve methoxy isomers and polymethoxy derivatives. Based on electronic and economic factors, we identify the optimal compounds for application as p-type hole-selective contacts in hybrid halide perovskite solar cells
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