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Previously unknown heterocyclic carbenes and their precursors containing a silicon atom in the side chain were prepared. Their structures were studied by multinuclear 1H, 13C, 15N, and 29Si NMR spectroscopy.

Novel 2-acetylamino-4-acetyl-5-aryl(heteryl)-1,3,4-thiadiazolines, 2-acetylamino-5-aryl(heteryl)-1,3,4-thiadiazoles, and some of their salts were prepared and studied by multinuclear 1H, 13C, 15N, 19F and 2D NMR spectroscopy. The acetylation of thiosemicarbazones is accompanied by ring closure to form the corresponding 1,3,4-thiadiazolines and 1,3,4-thiadiazoles. 15N NMR spectroscopy is a unique method for the identification of thiadiazole pyridinium salts. Copyright © 2007 John Wiley & Sons, Ltd.

The vicarious nucleophilic substitution of hydrogen in symmetrical and vicinal nitrotriazoles by 1,1,1-trimethylhydrazinium iodide in t-BuOK/DMSO was studied by ESR. In the ESR monitoring of the reactions the primary radical-anions of 4-nitro-2-phenyl-1,2,3-triazole and 1-methyl-3-nitro-1,2,4-triazole were detected and characterized. It was shown by NMR that the amination of 4-nitro-2-phenyl-1,2,3-triazole takes place exclusively in the triazole ring with the formation of 5-amino-4-nitro-2-phenyl-1,2,3-triazole. 1-Methyl-3-nitro-1,2,4-triazole, like 3-nitro-1,2,4-triazole, does not form amination products. A possible mechanism for the vicarious C-amination of nitrotriazoles and the formation of the radical-anions of the substrates is discussed.

A potential surface of rotational transformations of 1,3-di(silylmethyl)imidazol-2-ylidene and its halo-substituted analogs has been analyzed using quantum-chemical methods. Coordination interactions of the carbene center with Si-fragments have been studied. It is shown that the above interaction results in a structural reorganization of the silicon centers from the tetrahedral state to the trigonal–bipyramidal. This leads to a considerable stabilization of compounds in the planar state. The stabilization effect is strengthened by halogenation.

2-Benzoylmethylene-1,3,5-dithiazinium hydrobromides were prepared in high yield by the reaction of 1-bromo-2-benzoylacetylene with 2,4-dithiobiurete and its mono- and disubstituted derivatives in glacial AcOH. The ability of the compounds synthesized to undergo further chemical transformations has been studied.

The primary radical anions of substrate in the reactions of vicarious nucleophilic substitution of hydrogen in 1-methyl-4-nitropyrazole with 1,1,1-trimethylhydrazinium iodide and 4-amino-1,2,4-triazole in t-BuOK–DMSO were observed and identified by EPR monitoring. The probable mechanism of the substrate radical anions formation is discussed. Copyright © 2005 John Wiley & Sons, Ltd.

[4-Phenyl-2H-1,3-thiazin]-2-ylideneguanidinium perchlorate or acetoxytrifluoroborate respectively was obtained from the reaction of benzoylacetylene with N-amidinothiourea in glacial AcOH in the presence of an equimolar quantity of HClO4 or BF3⋅Et2O. These compounds underwent hydrolysis at the amidine unit on treatment with acid or base. For example, the perchlorate on heating in HClO4 was converted into 2-imino-4-phenyl-2H-1,3-thiazinium perchlorate, while treatment with aqueous NaOH in DMSO gave the free base - 6-phenyl-1,2-dihydropyrimidine-2-thione.

A number of N-alkylimidazoles and N-alkylbenzimidazoles were synthesized by reactions of imidazole and benzimidazole with alkyl halides. The reaction rate increases by a factor of 2 to 3 under conditions of microwave activation. Subsequent treatment of the resulting N-alkylazoles with alkyl halides afforded the corresponding 1,3-dialkylimidazolium and 1,3-dialkylbenzimidazolium halides.

The nucleophilic addition of 2,4-dithiobiurete, 1- and 1,4-substituted 2,4-dithiobiuretes (2 a-e) with benzoylacetylene (1) has been studied. 2-(Benzoylmethyl)-4-(R1-imino)-6-(R2-imino)dihydro-4H-1,3,5-dithiazinium perchlorates (3 a-e) are obtained in glacial acetic acid (AcOH) in the presence of equimolar quantities of HClO4. The reaction of benzoylacetylene with 1,5-diphenyl-2,4-dithiobiurete in either of MeOH, C6H6, or MeCN solvents proceeds non-selectively to give a mixture of products such as 2-(benzoylmethyl)-4,6-di(phenylimino)dihydro-4H-1,3,5-dithiazine (5), 2-(benzoylmethyl)-4-(β-benzoylvinyl)thio-3-phenyl-6-(phenylimino)-3,6-dihydro-2H-1,3,5-thiadiazine (8), 2-(benzoylmethyl)-1,3-diphenylhexahydro-1,3,5-triazine-4,6-dithione (7) and N-(β-benzoylvinyl)-N-phenylthioureas (6).

The modified Townes-Daily equation is shown to be better than the original one for frequencies of compounds having N-Cl bonds. Of the three semi-empirical methods AM 1, MNDO, PM 3, the first is preferable. The asymmetry parameters for the same compounds have been evaluated. The 35Cl NQR frequencies of two tautomers of N-chlorobenzotriazole are compared.

The correlation between the group dipole moments of substituents and the experimental values of ionization potentials has demonstarted that the position of the lower ionic π state of allylamine, allylmercaptane, allyl alcohol, and other organic allyl derivatives (except allyl bromide) was determined by the field effect. The empirically obtained conclusions were confirmed by semiempirical AM1 studies. The mechanism of destabilization of energetically unfavorable rotational isomers in the above series of compounds was considered, and it was found that this destabilization is caused mainly by electrostatic interaction.

Corrections accounting for the effect of the differences in p-electron energies on the electric field gradient are suggested and justified in the framework of Townes-Dailey theory. MNDO calculations of 31 chloro-containing molecules with full geometry optimization were used to evaluate the35Cl NQR frequencies. The correlational relationships between experimental and calculated NQR frequencies are compared.

The 35Cl NQR spectra of 3,5-dichloro-1,2,4-triazole derivatives have been examined. MNDO calculations of chloroazoles (imidazole, triazole) including their ionic forms have been carried out. In 3,5-dichloro-l,2,4-triazole complexation and protonation occur of position 4 at the triazole ring.

In molecules in the series Cl3CCH2CClRR', the substituents R and R' virtually do not affect the chlorine atoms of the Cl3C group, while the NQR frequency of the chlorine atom of the CClRR' group correlates satisfactorily with the σ* constants of these substituents. The regularities observed in the mutual influence of the atoms in the molecules of the studied series indicate that the previously assumed structure of some products of radical telomerization of Cl3CH with H2C=CHCl is erroneous.

35Cl NQR spectra (77 K) of 1:1 and 2:1 RR'CO-SnCl 4 are recorded and discussed. These spectra change in the course of time. At low temperatures either octahedral or trigonal-bipyramidal complexes (depending on the ratio of components and the nature of ligands) are formed. Frequently these systems contain a mixture of steric isomers or a mixture of complexes having different coordination numbers of the tin atom. In the solid state some complexes show a transition from one to another configuration.

Vicarious nucleophilic C-amination of nitrobenzene, 1-methyl-5-nitrobenzimidazole, and 1-methyl-6-nitrobenzimidazole in superbasic medium (potassium tert-butoxide-dimethyl sulfoxide) gave the corresponding amino-substituted derivatives. The yield of the amination product of 1-methyl-5-nitrobenzimidazole considerably increased in the presence of CuCl. ESR monitoring of these reactions revealed formation of primary radical anions from the substrates. Possible reaction mechanisms are discussed.

NQR frequencies and asymmetry parameters (η) of 35Cl chlorine-containing 1,5,2-diazaphosphorine derivatives are reported and discussed. NMDO calculations with total optimization of geometry have been carried out. The νcal and ηcal values, calculated by means of the Townes and Dailey theory, correlate well with the experimenal data.

The 35Cl NQR spectra of organyl(chloroalkyl) sulfides ClCH2S(CH2)nCH3, n = 0-11, Cl(CH2)mSR, m = 1 - 3 and alkyl(chloromethyl selenides ClCH2SeR (R = C2H5 , C3H7 ) have been obtained. In going from m = 1 to m = 2, the electron density on the CI atom in the series Cl(CH2)mYR increases when Y = S and decreases when Y = O.

The structure of the tetrachlorosilane-tetramethylurea complex suggested from NQR data is proved by X-ray crystallography; experimental data is compared with calculated values.

Silylotropy in 4-substitutedN-trimethylsilypyrazoles is studied by dynamic1H,13C, and29Si NMR spectroscopy. The catalytic 1,2-migration of a trimethylsilyl group in 4-halo-N-trimethylsilylpyrazoles was detected. Silylotropy inN-trimethylsilylpyrazoles in the presence of halogens of trimethylhalosilanes is believed to proceed through formation ofN,N′-bis(trimethylsilyl)pyrazolium salts, the barrier of silylotropy in pyrazoles being markedly reduced.

The reaction of ortho - and para -(alkoxyaryl)trimethylsilanes with tin tetrachloride proceeds under mild conditions with cleavage of the Si C bond and formation of the corresponding stannanes.

Within the framework of the Townes–Dailey theory some corrections have been suggested which make it possible to take account of the effect of differences in the p-electron energy on the electric field gradients and to improve the correlation between the experimental and theoretical NQR frequencies.

The obtained correlation between the 35Cl NQR frequencies for organic and the corresponding organometallic compounds CIMXX′X″ (M=C, Si, Ge, Sn) shows that transmission of the electronic effects of substituents across the M atom increases in the following order: Si

SnCl4 Complexes with methylaryl ethers and their 35Cl NQR spectra have been obtained. All these complexes, except SnCl4 · 1,2-(CH3O)2C6H4, have a trigonal-bipyramidal structure. The latter compound has an essentially distorted octahedral structure. One of the ligand oxygen atoms takes part in the formation of the SnCl4 complex with 1,3-, 1,4-(CH3O)2C6H4 and RNO2. These complexes have a trigonal-bipyramidal structure too.

The 35 Cl NQR spectra show that the adducts of tertiary amides R 2 NCOR' (R = CH 3 , C 2 H 5 ; R' = H, C 6 H 5 ) and phosphorus halides PCl 5 and POCl 3 have the structure: At the same time the reaction of (CH 3 )C 6 H 5 NCOCH 3 or (C 6 H 5 ) 2 NCOCH 3 with PCl 5 leads to organylchlorophosphonylhexachlorophosphate [RR'NCCl = CHPCl 3 ] + · PCl 6 − . The NQR spectrum of the adduct of DMF with PCl 3 does not agree with that suggested previously from IR- and PMR- spectra.

Asymmetry parameters for the electric field gradient at the 35Cl nuclei of polycrystalline Cl(CH2)3SnCl3 have been measured at 77 K. They are in agreement with a trigonal-bipyramidal structure for the molecule. The electron distribution of the axial chlorine atom in the SnCl3 group is almost axially symmetric whereas that of the two equatorial atoms and the chlorine atom in the Cl(CH2)3 group deviate noticeably from the axial symmetry. The deviation is mainly due to the interaction of the lone electron pair of the corresponding chlorine atom with the central tin atom.

N-Mono-alkylated imidazoles and benzimidazoles were prepared both by the traditional method and by microwave-assisted reaction. Their dialkylated salts were obtained, which are precursors for carbenes and novel 1,3-dialkylated imidazol-2-ilidenes and -benzimidazol-2-ilidenes.

Asymmetry parameters of the electric field gradients at the 35Cl nuclei in compounds of the RC6H4COCl series (R = H, 4-CH3, 2-, 3- and 4-COCl) have been measured at 77 K. They indicate a high asymmetry (> 20%) of the chlorine electron distribution in all the molecules studied. The substituent R in the aromatic ring has no significant effect on the asymmetry.

The condensation of PhCH2Cl with the liberation of HCl catalyzed by SnCl4, occurs in the PhCH2Cl-SnCl4. system. The proposal of the existence of a cis-octahedral complex, 2PhCH2Cl· SnCl4, was proved erroneous.

The asymmetry parameters of the electric field gradient at the 35Cl nuclei in polycrystalline compounds of the 2-, 3- and 4-XC6H4CH2Cl (X = CH3, Cl) series were measured at 77 K. The data obtained directly indicate the almost axial symmetry of the electric field gradient at the 35Cl nuclei, and the participation of the pσ electrons of the chlorine atom of the CICH2 group in the interaction with the geminal sp2 carbon atom in the molecules studied. The experimental η values allow a more precise assignment of the lines in the NQR spectrum of 3-ClC6H4CH2Cl.