Rinat R. Aysin

The interaction of five-membered hafnacyclocumulene complex 1Hf with ketones was investigated. The reaction outcome depends on the conditions and the ketone substituents. Under UV irradiation, insertion can be halted at one or two ketone molecules inserted into Hf–C bonds, affording hafnadihydrofuran 2Ph or the nine-membered dioxahafnacyclocumulene 3Fl. Under thermal conditions, the reaction of 1Hf with ketones revealed, for the first time, ketone insertion into one or two Cp–Hf bonds of the metallocene moiety. In the reaction with benzophenone, the corresponding insertion product 4Phb was isolated, and its structure was confirmed by SC-XRD. Products resulting from the insertion of benzophenone or fluorenone into the Cp–Hf bonds of the metallocene fragment of the hafnacyclocumulene were also characterized. A ketone insertion mechanism into the Cp–Hf bonds was proposed based on quantum chemical calculations at the DLPNO–CCSD(T)/Def2-TZVP//r2-SCAN-3c/Def2-TZVP level of theory. The calculation results revealed that the ketone undergoes insertion via η1-type of Cp–Hf bond. Furthermore, benzophenone and fluorenone also insert into the Cp–Hf bonds of hafnocene diphenolates by the same manner. The results obtained allow understanding the general deactivation mechanism in metallocene catalytic processes under interaction with carbonyl compounds.

A series of previously unknown fused benzodithiinochalcogenadiazoles, benzo[5,6][1,4]dithiino[2,3‑c][1,2,5]thia- and oxadiazoles, and its N-oxide, have been synthesized starting from readily available dichloroglyoxime via a key intermediate, benzo[b][1,4]dithiine-2,3‑dione dioxime. Benzo[5,6][1,4]dithiino[2,3-c][1,2,5]thiadiazole was successfully prepared using disulfur dichloride in DMF, while the corresponding [1,2,5]oxadiazole was unexpectedly obtained by dehydration of starting dioxime with selenium dioxide. Oxidation of benzo[b][1,4]dithiine-2,3‑dione dioxime with concentrated nitric acid gave the 1,2,5-oxadiazole N-oxide derivative. The molecular structures of all three compounds were unambiguously confirmed by single‑crystal X‑ray diffraction, which revealed a strong dependence of the molecular planarity on the nature of the chalcogenadiazole ring and the presence of the exocyclic N→O bond. DFT calculations using the EDDB method demonstrated that the compounds do not form a unified aromatic system. The thiadiazole ring shows the highest aromaticity, whereas the oxadiazole ring is only weakly aromatic. Electron affinity (EA) values, calculated at the DLPNO‑CCSD(T) level, are moderate for thia- and oxadiazoles, but increase substantially for 1,2,5-oxadiazole N-oxide, correlating with spin density localization in the corresponding anion radicals. These findings provide a basis for fine‑tuning the electronic and structural properties of benzodithiinochalcogenadiazoles by chalcogen variation, which may be of interest for the design of functional materials in optoelectronics and related fields.

The metalation of 3,6-di- tert -butyl-1,8-bis-(2,4,6-triisopropylphenyl)-9 H -carbazole ( 1 ) with n -BuLi, t -BuLi or Me ₃ SiCH ₂ Li (1 : 2) in heptane affords binuclear ionic complexes containing monomeric n -BuLi, t -BuLi and Me ₃ SiCH ₂ Li units.

In this work, an approach enabling the synthesis of η²-alkene lithium complexes (Carb^2,4,6-iPr)Li(η²-L) (L = 1-octene, cyclohexene) is elaborated. For 1,5-hexadiene, the same approach results in a binuclear μ-η²:η²-diene complex. The QTAIM parameters reveal the electrostatic nature of the Li-alkene interaction. When treated with cyclohexane, alkene ligands in (Carb^2,4,6-iPr)Li(η²-L) are readily replaced to afford the Li-alkane complex (Carb^2,4,6-iPr)Li(κ²-C₆H₁₂) featuring anagostic Li···H interactions. The reverse reaction readily proceeds in the presence of excess alkene. The QTAIM and LED analyses performed at the DLPNO-CCSD(T) level show a small difference between the complexes in the total dispersion contribution (16.0-18.5 kcal/mol) and interaction energy for Li-alkene (∼3.5 kcal/mol) or Li-C₆H₁₂ (∼4 kcal/mol). These values suggest the presence of an equilibrium between these entities, which can be readily shifted by the presence of an excess of alkene or alkane. (Carb^2,4,6-iPr)Li(η²-L) and (Carb^2,4,6-iPr)Li(κ²-C₆H₁₂) are transformed into η²-arene complexes upon treatment with benzene; however, a reverse reaction is not possible at room temperature.

In the chemistry of bio-based furans, the Diels–Alder reaction plays an important role as a renewable route for the synthesis of fuels, fine chemicals, and monomers. Nonetheless, the unfavorable kinetic and thermodynamic parameters inherent to the Diels–Alder reaction involving furans as dienes often lead to the reversibility of cycloaddition, resulting in decreased equilibrium conversion and diastereoselectivity. In this study, we present a new strategy for overcoming the problem of reversibility in chemical reactions. We demonstrate that conducting the reaction under solvent-free conditions can facilitate the transition from a molten state formed by the initial reactants to a solid phase containing the reaction product along with an excess of the initial substrate. According to our results, such a liquid-to-solid transition of the reaction mixture can lead to exceptionally high conversion and diastereoselectivity in the furan–maleimide Diels–Alder reaction, particularly for challenging electron-poor furanic substrates. Our approach enables the reversible furan–maleimide Diels–Alder reaction to be performed in a cleaner and more environmentally friendly manner, free from the complexities associated with the use of solvents and the need for purification from side products.