Synthesis, Structures, and Electronic Properties of O- and S-Heterocyclic Carbene Complexes of Iridium, Copper, Silver, and Gold

O- and S-heterocyclic carbenes (OHCs, SHCs) are shown experimentally and computationally to be stronger pi acceptors than NHCs and lack, of course, substituents at the heteroatoms. These different electronic and steric characteristics make OHCs and SHCs interesting ligands for coordination chemistry. Convenient synthetic routes are presented to access their iridium(I), iridium(III), and coinage-metal(I) (Cu, Ag, Au) complexes in good yields by means of dissociation of olefins, deprotonation of precursor salts, and transmetalation from a silver carbene complex Molecular structures and detailed bonding analyses of these complexes are presented.Peer reviewe

Співставлення чіткого та нечіткого підходів до розв’язку задач інформаційної безпеки

Проведено порівняння чіткого та нечіткого підходів із метою виявлення їх спільних рис та відмінностей. У задачі розподілу ресурсів захисту інформації проаналізовано принципи формування функцій належності до нечітких множин і їх вплив на кінцеві результати. Показано, що нечіткий підхід дає змогу оптимізувати показники системи захисту інформації за рахунок раціонального вибору функцій належності, які відображають основну характеристику об’єктів — їх динамічну вразливість. На прикладі системи з двох об’єктів із різними вразливостями встановлені умови, за яких досягається найвищий рівень співпадіння результатів у разі використання двох підходів. Методика може бути використана під час розрахунку допустимих витрат в інформаційних системах із довільною кількістю об’єктів, котрі відрізняються кількістю розміщеної інформації, вразливістю та рівнем допустимих втрат. Окреслені шляхи подальшого застосування приведеної методики в задачах інформаційної безпеки.Проведено сравнение четкого и нечеткого подходов с целью выявления их общих черт и различий. В задаче распределения ресурсов защиты информации проанализированы принципы формирования функций принадлежности к нечетким множествам и их влияние на конечные результаты. Показано, что нечеткий подход дает возможность оптимизировать показатели системы защиты информации за счет рационального выбора функций принадлежности, которые отражают основную характеристику объектов — их динамическую уязвимость. На примере системы из двух объектов с различными уязвимостями установлены условия, при которых достигается наивысший уровень совпадения результатов при использовании двух подходов. Методика может быть использована при расчете допустимых затрат в информационных системах с произвольным количеством объектов, которые отличаются объемом размещенной информации, уязвимостью и уровнем допустимых потерь. Обозначены пути дальнейшего применения приведенной методики в задачах информационной безопасности.A comparison of explicit and fuzzy approaches to identify their similarities and differences is carried out. In the problem of distribution of resources of information protection the principles of the formation of the membership functions to the fuzzy sets and their effect on the final results are analyzed. It is shown that the fuzzy approach gives the possibility to optimize the indicators of the system of information security through a rational choice of the membership functions, which reflect the basic characteristic of the objects - their dynamic vulnerability. Through the example of the system of two objects with different vulnerabilities the conditions under which the highest level of results coincidence is achieved using two approaches are established. The technique can be used when calculating the eligible costs of information systems with an arbitrary number of objects that have different volume of the placed information, vulnerability and level of acceptable losses. The ways of further application of the method in problems of information security are identified

Catalytic Dehydrogenation of Amine-Boranes using Geminal Phosphino-Boranes

The reaction of the intramolecular frustrated Lewis pair (FLP) tBu2PCH2BPh2 with the amine-boranes NH3·BH3 and Me2NH·BH3 leads to the formation of the corresponding FLP-H2 adducts as well as novel five-membered heterocycles that result from capturing the in situ formed amino-borane by a second equivalent of FLP. The sterically more demanding tBu2PCH2BMes2 does not form such a five-membered heterocycle when reacted with Me2NH·BH3 and its H2 adduct liberates dihydrogen at elevated temperatures, promoting the metal-free catalytic dehydrogenation of amine-boranes.Peer reviewe

On the electronic impact of abnormal C4-bonding in N-heterocyclic carbene complexes

Sterically similar palladium dicarbene complexes have been synthesized that comprise permethylated dicarbene ligands which bind the metal center either in a normal coordination mode via C2 or abnormally via C4. Due to the strong structural analogy of the complexes, differences in reactivity patterns may be attributed to the distinct electronic impact of normal versus abnormal carbene bonding, while stereoelectronic effects are negligible. Unique reactivity patterns have been identified for the abnormal carbene complexes, specifically upon reaction with Lewis acids and in oxidative addition-reductive elimination sequences. These reactivities as well as analytical investigations using X-ray diffraction and X-ray photoelectron spectroscopy indicate that the C4 bonding mode increases the electron density at the metal center substantially, classifying such C4-bound carbene ligands amongst the most basic neutral donors known thus far. A direct application of this enhanced electron density at the metal center is demonstrated by the catalytic H₂ activation with abnormal carbene complexes under mild conditions, leading to a catalytic process for the hydrogenation of olefins

New Insights in Frustrated Lewis Pair Chemistry with Azides

The geminal frustrated Lewis pair (FLP) tBu(2)PCH(2)BPh(2) (1) reacts with phenyl-, mesityl-, and tert-butyl azide affording, respectively, six, five, and four-membered rings as isolable products. DFT calculations revealed that the formation of all products proceeds via the six-membered ring structure, which is thermally stable with an N-phenyl group, but rearranges when sterically more encumbered Mes-N-3 and tBu-N-3 are used. The reaction of 1 with Me3Si-N-3 is believed to follow the same course, yet subsequent N-2 elimination occurs to afford a four-membered heterocycle (5), which can be considered as a formal FLP-trimethylsilylnitrene adduct. Compound 5 reacts with hydrochloric acid or tetramethylammonium fluoride and showed frustrated Lewis pair reactivity towards phenylisocyanate.Peer reviewe

Facile Synthesis of Tuneable Azophosphonium Salts

Azophosphonium salts have a facile synthesis and can be readily tuned at the para position of the aryl group and at the phosphorus position with the use of bulky phosphines, leading to a range of coloured compounds. A relation between the Hammett sigma(+)(para) constant and the colour and P-31 NMR chemical shift was explored. The compounds were characterised by NMR spectroscopy, UV/Vis spectroscopy and single-crystal X-ray structure crystallography.Peer reviewe

Protic NHC Iridium Complexes with beta-H Reactivity-Synthesis, Acetonitrile Insertion, and Oxidative Self-Activation

Protic NHC iridium complexes, obtained from the corresponding azido-phenylene-isocyanide precursor complexes, were investigated for ligand-based reactivity. Under redox-neutral conditions, acetonitrile inserts into the N-H bonds to provide kappa(2)-NHC-imidoyl ligand-based complexes, while under reductive conditions the complex also expels one N-H proton to provide the corresponding deprotonated analogues. Using zinc as a reductor activates the NHC-iridium complex to form an asymmetric bimetallic iridium hydrido complex, in which two anionic N-deprotonated NHCs bridge the bimetallic core. X-ray crystal structures are reported for the azido-phenylene-isocyanide precursor complex, the protic NHC complex, and the asymmetric bimetallic iridium hydride complex. Density functional computations and a QTAIM analysis of the bimetallic iridium hydrido complex are provided.Peer reviewe

Valence isomerization of 2-phospha-4-silabicyclo[1.1.0]butane: a high-level ab initio study

The rearrangements for 2-phospha-4-silabicyclo[1.1.0]butane, analogous to the valence isomerization of the hydrocarbons bicyclobutane, 1,3-butadiene, and cyclobutene, were studied at the (U)QCISD(T)/6-311+G**//(U)QCISD/6-31G* level of theory. The monocyclic 1,2-dihydro-1,2-phosphasiletes are shown to be the thermodynamically preferred product, in contrast to the isomerization of the hydrocarbons, which favors the 1,3-butadiene structure. Furthermore, an unprecedented direct isomerization pathway to the 1,2-dihydro-1,2-phosphasiletes was identified. This pathway is competitive with the isomerization via the open-chain butadienes and becomes favorable when electron-donating substituents are present on silicon

Altered spin state equilibrium in the T309V mutant of cytochrome P450 2D6: a spectroscopic and computational study

Cytochrome P450 2D6 (CYP2D6) is one of the most important cytochromes P450 in humans. Resonance Raman data from the T309V mutant of CYP2D6 show that the substitution of the conserved I-helix threonine situated in the enzyme’s active site perturbs the heme spin equilibrium in favor of the six-coordinated low-spin species. A mechanistic hypothesis is introduced to explain the experimental observations, and its compatibility with the available structural and spectroscopic data is tested using quantum-mechanical density functional theory calculations on active-site models for both the CYP2D6 wild type and the T309V mutant