A novel organosilicon complex of N-acetylvaline was synthesized by the reaction of the relative disiloxane derivative with BF3 etherate. According to X-ray and NMR data, the silicon atom of the final product is pentacoordinated in both the solid state and solution. The coordination state of silicon was correctly predicted by quantum-chemical calculations.

Anionic complexes LSi(Cat(R))(2) (L is a chelate N-methyl-N-(acetamido) methyl-C,O group or (2-oxo-1-hexahydroazepinyl)methyl-C,O group; Cat(R) is a substituted catecholate ligand) were studied by quantum chemistry at the PBE0/6-311G(d,p) and RI-MP2/def2-TZVPP levels with inclusion of nonspecific solvation using the PCM model. It was shown that the nature of substituents in the catecholate phenyl ring and the L group weakly influences the geometry of the coordination environment of the silicon atom. The higher the electron-withdrawing effect and the number of substituents in the catecholate ligands, the higher the vertical or adiabatic ionization potentials. It was established that the formation of oxidized forms of the complexes LSi(Cat(R))(2) is characterized by weakening of the Si-O bonds between the silicon atom and the Cat(R) (Cat(R)-2) ligand opposite to the Si-O bond with the group L and by shortening of the Si-O bonds between the silicon atom and the other catecholate ligand (Cat(R)-1). An analysis of the average local ionization energies and a topological analysis of the electron localization function showed the Cat(R)-2 ligand is less sensitive to the interaction with free radicals than Cat(R)-1 due to redistribution of electron density from the region of its oxygen atoms and phenyl ring.

Crystal structures of fluorinated alkyl tosylates TsOCH2CF2CHFCF3 and TsOCH2(CF2)(3)CHF2 have been characterized by X-ray diffraction and quantum chemical calculations. The calculations have revealed the stabilization of head-to-tail conformation for TsOCH2CHF-CF2CF3 due to intramolecular F center dot center dot center dot pi and C-H center dot center dot center dot pi interactions. Alternatively, for TsOCH2(CF2)(3)CHF2 these interactions cannot be responsible for the stabilization of head-to-tail con-formation, thus the linear conformation is proved to be more stable.

The peculiarities of interatomic interactions formed by fluorine atoms were studied in four tosylate derivatives p-CH3C6H4OSO2CH2CF2CF3 and p-CH3C6H4OSO2CH2(CF2)nCHF2 (n = 1, 5, 7) using X-ray diffraction and quantum chemical calculations. Compounds p-CH3C6H4OSO2CH2(CF2)nCHF2 (n = 1, 5) were crystallized in several polymorph modifications. Analysis of intermolecular bonding was carried out using QTAIM approach and energy partitioning. All compounds are characterized by crystal packing of similar type and the contribution of intermolecular interactions formed by fluorine atoms to lattice energy is raised along with the increase of their amount. The energy of intra- and intermolecular F…F interactions is varied in range 0.5–13.0 kJ/mol. Total contribution of F…F interactions to lattice energy does not exceed 40%. Crystal structures of studied compounds are stabilized mainly by C-H…O and C-H…F weak hydrogen bonds. The analysis of intermolecular interactions and lattice energies in polymorphs of p-CH3C6H4OSO2CH2(CF2)nCHF2 (n = 1, 5) has shown that most stabilized are characterized by the least contribution of F…F interactions.

Derivatives of the amino acids sarcosine and proline – triflates TsN(Me)CH2C(O)N(Me)-CH2SiMe2OTf and Ns–Pro–N(Me)CH2SiMe2OTf (Ns is 4-NO2C6H4SO2) – were synthesized by the reaction of trimethylsilyl triflate with halosilanes prepared previously. Bromide NsNHCH(Me)C(O)N(Me)CH2SiMe2Br was synthesized by the cleavage of the Si–O–Si moiety of the appropriate disiloxane with excess acetyl bromide. The X-ray diffraction study of these compounds and of the previously characterized bromide TsN(Ac)CH2C(O)N(Me) CH2SiMe2Br showed that the Si–O coordination bond lengths in the triflates are 1.7692(14)– 1.8623(14) Å. The interatomic distances between the bromine and silicon atoms are 2.7095(8) and 2.9704(7) Å, which indicates that these bonds are weak. To elucidate the nature of Si…X bonding (X = OTf, Br), the topological analysis of electron density was performed and 29Si NMR chemical shifts were calculated. The interatomic Si…X interaction in triflate TsN(Me)CH2C(O)- N(Me)CH2SiMe2OTf and bromide TsN(Ac)CH2C(O)N(Me)CH2SiMe2Br is weak. In triflate Ns–Pro–N(Me)CH2SiMe2OTf and bromide NsNHCH(Me)C(O)N(Me) CH2 SiMe2Br, the Si…X interaction is significantly stronger and corresponds to a weak coordination bond. Hence, the tosylates can be considered as salts, whereas the para-nitrobenzenesulfonyl derivatives are monochelated five-coordinate silicon complexes.

Anionic five-coordinate complexes with two bis-O,O’-chelating ligands bearing α-hydroxy acid moieties, dicyclohexylammonium salts $$\text{Cy}_{2}\text{NH}_{2}{^+}\{\text{PpnCH}_2\text{Si}[\text{OCR}_2\text{C}\text{(O)O]}_2\}^-$$ (Cy is cyclohexyl, PpnCH2 is 4-methyl-2,5-dioxopiperazin-1-ylmethyl, R = Me, Ph), were synthesized by esterification of alkoxysilane PpnCH2Si(OMe)3 with α-hydroxy acids (dimethyl- and diphenylgylcolic acids) in the presence of dicyclohexylamine. The five-coordinated state of the silicon atom in the resulting compounds in solution was confirmed by 29Si NMR spectroscopy. According to the X-ray diffraction data, the synthesized compounds contain the SiCO4 coordination unit.

The structures and stereodynamic behavior of (O -> Si)-chelate methyldifluorosilanes in solutions were studied by multinuclear (H-1, C-13, F-19, Si-29) and 2D (COSY, HETCOR H-1, C-13) NMR spectroscopy. The range of studied complexes included amides RC(O)N(R')CH2SiMeF2 [R = Ph, R' = H (1a); R = R' = Me (1b); R = Me, R' = CHMePh (1c)], lactams LCH2SiMeF2 (L = 2-oxoazepan-1-yl (2a), 2,2-dimethyl-4-oxo-2H-benzo[1,3] oxazin-3-yl (2b) or 4-methyl-2-oxoquinolin-l-yl (2c)] and the six-membered imide Im(6)CH(2) [2,6-dioxopiperidin-1-yl (3)]. The pentacoordination of silicon atoms in all studied compounds was confirmed by NMR study in solutions and single-crystal X-ray studies of complexes 1c, 2a, 2c and 3. The temperature dependency observed for the F-19 NMR signals in solution was explained by the ligand exchange in the coordination environment of silicon atoms (permutational isomerization) and used for determining the activation parameters of this process by F-19 DNMR. Quantum-chemical calculations for various isomers of complexes 1c, 2a, 2c and 3 suggested the "turnstile rotation" as the most likely mechanism for the observed stereodynamic processes. (C) 2018 Elsevier B.V. All rights reserved.

A series of mono-, bis-, and tris-substituted lactamomethyl derivatives of diphenols were synthesized. The solution and solid-state structures of these compounds were confirmed by IR and NMR spectroscopy and X-ray diffraction. The in silico evaluation indicated a high probability that these compounds have various biological activities.

Silylmethylation of N-acetylvaline with the ClCH2SiMe2Cl(Me3Si)(2)NH system gave the previously unknown 2-silamorpholin-6-one derivative, whose hydrolysis in aqueous ethanol produced bis-acetylvaline-containing disiloxane. The X-ray diffraction study and quantum chemical calculations demonstrated that both silicon atoms in the final product are four-coordinated.

Pentacoordinated monofluorosilanes R1SO2NHCHR2C(O)N(Me)CH2SiMe2F containing moieties of N′-methyl-N-(organosulfonyl)-2-amino acid amides of glycine, alanine, and leucine as C,O-chelating ligands were synthesized via the reaction of corresponding disiloxanes with BF3•Et2O. The structures of obtained compounds were investigated by single-crystal X-ray diffraction analysis.

A protocol to access ferrocenecarboxylic acid via carboxylation of ferrocene with carbon dioxide in the presence of aluminum chloride was elaborated. An efficient microwave-assisted synthesis of ferrocenoyl hydrazones by condensation of ferrocene carbohydrazide with carbonyl compounds was developed. Structures of the synthesized compounds were examined by NMR spectroscopy and mass spectrometry. Structures of N ´-(4-chlorobenzylidene)ferrocenecarbohydrazide, N ´-(4-methoxybenzylidene)ferrocenecarbohydrazide, and N ´-(2-hydroxybenzylidene)ferrocenecarbohydrazide were determined by X-ray diffraction analysis. Synthesized compounds were found to have no toxicity against P. aeruginosa , E. coli , S. aureus , B. subtilis , M. rubrum , and C. albicans .

A novel pyridine-azacrown ether amide macrocycles comprising pyridine or carboxylic pendant arms were synthesized. The protonation constants of the compounds and the stability constants of their complexes with a wide range of metal ions (Ag+, Cu2+, Zn2+, Cd2+, Ni2+, Pb2+, Y3+, Eu3+, Lu3+) were determined by potentiometric method. The different complexes of macrocycles with cations, including HML, ML and ML(OH)n were found to form. The increase of the stability of the complexes provides the presence of carboxyl substituents in pyridine-azacrown ether amide macrocycles; the values for the Cu2+, Ni2+ and Pb2+ complexes of ligand containing three carboxylic arms are exceptionally high. Single crystal structures of a few complexes with Cu2+ and Pb2+ were determined. In all complexes, the metal centre exhibit a strong coordination with amine N-atoms and arm’s ligand groups. The rigid structure of pyridine-2,6-dicarbamide fragment and an open macrocyclic cavity provide a possibility to fast kinetics of complex formation.

The photophysical properties of naphthalimide dyes NI1-3 with electron releasing 4-methoxy-(NI1), 3,4-dimethoxystyryl-(NI2) and dimethylaminostyryl (NI3) groups are examined in a variety of protic and aprotic solvents. All compounds demonstrate positive solvatochromism in the steady-state absorption and fluorescence spectra. The analysis of the dependence of the Stokes shift on the polarity of the solvent using the Lippert-Mataga equation allowed us to determine the change in the dipole moment upon excitation. The obtained data correspond to the formation of highly polar charge transfer states. Based on the transient absorption spectra and time-resolved fluorescence measurements, the presence of two different emissive states was definitely proved. The primarily formed planar Local Excited (LE) state dominates in non-polar solvents like cyclohexane and toluene where it relaxes mostly through fluorescence and E, Z-isomerisation pathways. In polar solvents, an alternative relaxation channel emerges that consists of twisting around single bond between styryl and naphthalimide fragments, which leads to the formation of a Twisted Intramolecular Charge Transfer (TICT) state. The factors affecting the fluorescence of TICT states are discussed. The observed spectral effects are rationalized using quantum-chemical calculations, X-ray data and NMR spectroscopy.

A reaction of bicyclic 2-sila-5-piperazinone, 2,2,4-trimethyl-1,4-diaza-2-silabicyclo-[4.3.0]nonan-5-one containing a proline moiety, and N-tosylglycine acyl chloride with subsequent hydrolysis of the primary unstable product to the intermediate disiloxane and its treatment with BF3•OEt2 furnished a first representative of pentacoordinate C,O-chelate halosilanes with a dipeptide fragment, namely, Ts—Gly—(S)-Pro—N(Me)CH2SiMe2F.

AbstractThe title process provides the first successful synthetic approach to 1H‐2,3‐benzoxazine 3‐oxides.

Regioselectivity of the HBF4-catalyzed ferrocenylalkylation of 2-mercaptobenzoxazole in two phase aqueous organic solvent mixture was studied. The reaction proceeds regioselectively at the heterocyclic nitrogen atom. Structures of the synthesized compounds were established by 2D NMR technique. Structure of 3-(1-ferrocenylbenzyl)benz[d]oxazol-2-thione was elucidated by X-ray diffraction.

(O→Si)-Chelate difluorides R3R2NCH(R1)C(O)N(CH2SiMe2F)2, were synthesized by silylmethylation of amides R3R2NCH(R1)C(O)NH2, subsequent hydrolysis of unstable dichlorides into 2,6-disilamorpholines and the reaction of the latter compounds with BF3·Et2O.

An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.