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The scopes and limitations of theoretical methods for estimating various NMR metrics of NHCs are considered on a wide range of model NHCs and their derivatives, using a number of computational approximations. On the whole, the most reliable, from the point of view of predictability and insusceptibility to additional effects, are 31 P/ 13 C NMR shifts of NHC-phosphinidene adducts and 13 C CSs of carbenes themselves. The method based on the analysis of 77 Se CS NHC-selenoureas has some limitations since the observed NMR parameters can also be modulated by exchange effects due to their formation with non-classical hydrogen bonds. As for HEP, since the delicate balance of electron distribution between Pd and two carbon centers can nonlinearly affect relativistic spin-orbit effects, the accuracy of the estimation of this metric may still be limited. 13 C CSs of NHC-azolium salts do not seem to be reliable, since the observed values are strongly influenced by the effects of the exchange between different forms with counterions, which are difficult to estimate correctly.

In this study, comparative analysis of calculated (GIAO method, DFT level) and experimental 31 P NMR shifts for a wide range of model palladium complexes showed that, on the whole, the theory reproduces the experimental data well. The exceptions are the complexes with the P=O phosphorus, for which there is a systematic underestimation of shielding, the value of which depends on the flexibility of the basis sets, especially at the geometry optimization stage. The use of triple-ζ quality basis sets and additional polarization functions at this stage reduces the underestimation of shielding for such phosphorus atoms. To summarize, in practice, for the rapid assessment of 31 P NMR shifts, with the exception of the P=O type, a simple PBE0/{6-311G(2d,2p); Pd(SDD)}//PBE0/{6-31+G(d); Pd(SDD)} approximation is quite acceptable ( RMSE = 8.9 ppm). Optimal, from the point of view of "price-quality" ratio, is the PBE0/{6-311G(2d,2p); Pd(SDD)}//PBE0/{6-311+G(2d); Pd(SDD)} ( RMSE = 8.0 ppm) and the PBE0/{def2-TZVP; Pd(SDD)}//PBE0/{6-311+G(2d); Pd(SDD)} ( RMSE = 6.9 ppm) approaches. In all cases, a linear scaling procedure is necessary to minimize systematic errors.

Synthesis and structural and photophysical characterization of platinum dihalogenide complexes formulated as [PtHal 2 L 2 ], where Hal = Cl and I, with different 10-(aryl)phenoxarsine ligands such as 10-( p -chlorophenyl)phenoxarsine, 10-( p -tolyl)phenoxarsine, and 10-(phenyl)phenoxarsine are reported. The structures of complexes were determined by NMR spectroscopy, mass spectrometry, and X-ray analysis. Cis/trans isomerism of the complexes in solution was studied by NMR spectroscopy. In the solid state, under UV irradiation, platinum diiodide trans complexes exhibit an intense orange-red emission, which was attributed to a metal halide-centered triplet state. The UV/vis absorption and emission properties were studied and rationalized by density functional theory (DFT) and time-dependent DFT calculations.

In lumazines, deazalumazines and pyrimidines, there are extremely low-energy "rare" tautomers (<2.3 kcal/mol), this fact perfectly explains the observed mobility of usually "non-labile" protons of methyl groups in such systems. In general, the dependence of tautomeric preference on structure correlates well with experimental findings. Thus, the activity of alkyl groups during biological transformations may be due to the presence of the corresponding thermodynamically stable tautomers., (Copyright © 2021 Elsevier Inc. All rights reserved.)

New uncharged conjugates of 6-methyluracil derivatives with imidazole-2-aldoxime and 1,2,4-triazole-3-hydroxamic acid units were synthesized and studied as reactivators of organophosphate-inhibited cholinesterase. Using paraoxon (POX) as a model organophosphate, it was shown that 6-methyluracil derivatives linked with hydroxamic acid are able to reactivate POX-inhibited human acetylcholinesterase (AChE) in vitro. The reactivating efficacy of one compound (5b) is lower than that of pyridinium-2-aldoxime (2-PAM). Meanwhile, unlike 2-PAM, in vivo study showed that the lead compound 5b is able: (1) to reactivate POX-inhibited AChE in the brain; (2) to decrease death of neurons and, (3) to prevent memory impairment in rat model of POX-induced neurodegeneration., (Copyright © 2019 Elsevier Masson SAS. All rights reserved.)

A straightforward synthesis of P-chiral polycyclic phosphines by an asymmetric Diels-Alder reaction of 1-alkyl-1,2-diphospholes and (5R)-(l-menthyloxy)-2(5H)-furanone (MOxF) is presented. The [4 + 2] cycloaddition reaction of 1,2-diphospholes 1-3 with MOxF (4) proceeded with high diastereoselectivity (de up to 90%) resulting in the corresponding enantiopure anti-endo-1,7-diphosphanorbornenes 5a-7a. The absolute configuration of 5-7 was proved by a variety of 1D/2D NMR correlation methods. The use of the anti-endo-1,7-diphosphanorbornene 5a in the Pd-catalyzed asymmetric allylic alkylation of cinnamyl acetate 8 with cyclic β-ketoesters 9a,b provided up to 52% ee.

The first representative of the specific RSSR isomer of 14-membered tetrakisphosphine has been obtained instead of the RRRR/SSSS isomer predicted according to the empirical rule formulated recently. The geometry of the obtained 14-P 4 N 2 is preorganized for the dicopper complex formation with the unique coordination mode in the row of P 4 N 2 corands.