Structure,vibrational spectra,and energetic stability of LnX<Stack><Subscript>4</Subscript><Superscript>−</Superscript></Stack> ions (Ln=La,Lu; X=F,Cl, Br,I)

Molecular structure and properties of La and Lu tetrahalide ions LnX ₄ ^– ) are studied by the configuration interaction singles-and-doubles method augmented with quadruple excitation correction (CISD+Q) and by the fourth-order Möller-Plesset perturbation theory with account for single, double, triple, and quadruple excitations (SDTQ-MP4). The atomic inner shells are described by Stevens relativistic effective core potentials. Valence basis sets are augmented with diffuse s-, p-, and polarization d-, f-, and g-functions. The equilibrium configuration of nuclei in LnX ₄ ^– ions was found to be tetrahedral. The equilibrium internuclear distances, quadratic force constants, vibrational frequencies, and IR intensities of LnX ₄ ^– ions are compared with the corresponding parameters of La and Lu trihalide molecules (LnX₃), calculated within the same approximations. Regularities in the behavior of molecular parameters on going along the LnF ₄ ^– LnCl ₄ ^– LnBr ₄ ^– LnI ₄ ^– series and from La compounds to Lu compounds are revealed. Heights of the energy barriers to the LnX ₄ ^– inversion through the square planar structures (T _d D _4h T _d ) are evaluated: 100–110 and 130–150 kJ/mol for LaX ₄ ^– and LuX ₄ ^– , respectively. Enthalpies of dissociation reactions LnX ₄ ^– LnX₃+X^– are calculated and the results obtained are compared with the available experimental data.Translated from Koordinatsionnaya Khimiya, Vol. 31, No. 3, 2005, pp. 218–228.Original Russian Text Copyright © 2005 by Solomonik, Smirnov, Mileyev.This revised version was published online in April 2005 with a corrected cover date.This revised version was published online in April 2005 with a corrected cover date.     

Synthesis of brominated 2-(tert-butyl-NNO-azoxy)anilmes

2-(tert-Butyl-NNO-azoxy)aniline was prepared by selective reduction of 2-(tert-butyl-NNO-azoxy)nitrobenzene. Its bromination yielded the correspondingpara-bromo- andortho, para-dibromoanilines (3a,b).meta-Bromoanilines (6a,b) were synthesized by selective replacement of theortho-bromine atoms in ortho,para-bromo(tert-butylazoxy)benzenes (5a,b) by ammonia in toluene under pressure.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1620–1623, September, 1994.This work was carried out with the financial support of the Russian Foundation for Basic Research (Project No. 93-03-18461).     

Effect of the coordination sphere of d<Superscript>0</Superscript> metallocene on triplet-triplet energy transfer

The triplet nature of rare long-lived states of d⁰ metallocenes formed upon ligand-to-metal energy transfer was confirmed by studies of triplet-triplet charge transfer in biscyclopentadienyl complexes Cp₂MCl₂ (M = Zr (1), Hf (2)). The interaction between precatalysts and substrates of catalytic polymerization systems, viz., complexes 1 and 2 and unsaturated hydrocarbons (alkenes and dienes), was studied in the region of concentrations close to catalytic values. For organometallic π-complexes, it has been shown for the first time that, in the case of the unsaturated hydrocarbons, the efficiency of energy transfer obeys the Perrin equation. The process occurs at distances R ₀ close to the diameter of the interacting molecules and is well described by the exchange-resonant mechanism of interaction. In the case of the cyclopentadiene-Cp₂MCl₂ (M = Zr, Hf) systems, R ₀ = 14.6 Å. A linear relationship between the critical radius of the quenching sphere R ₀ and the number of carbon atoms in a linear α-olefin has been revealed for the first time and evidences the formation of a π-complex between the precatalyst and substrate molecules. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 35–39, January, 2007.     

Kinetic Study of the Heck Reaction by the Method of Competing Reactions

The method of competing reactions is used to measure the isotope effect in styrene phenylation by iodobenzene. The kinetics of styrene, methyl acrylate, and methyl methacrylate phenylation is studied. Experimental data suggest that the step of alkene insertion is relatively fast, while the subsequent step that involves C–H bond dissociation is rate-limiting. The kinetic parameters of the process point to the dependence of the rate-limiting step of the catalytic cycle on the concentrations of base and alkene. These results are consistent with the existing hypothesis that the step of -elimination of palladium hydride is present in the mechanism.     

1,1,4,4-Tetranitrobutane-2,3-diol and its derivatives. 5. Reaction of 1,1,4,4-tetranitrobutane-2,3-diol with formaldehyde; synthesis and crystal structure of 4,4-dinitro-2,3-dihydroxytetrahydrofuran

1,1,4,4-Tetranitrobutane-2,3-diol reacts with formaldehyde, forming 2,2-dinitropropane-1,3-diol or a cyclic ether — 4,4-dinitro-2,3-dihydroxytetrahydrofuran — as a function of the reaction conditions.Institute of Chemical Physics, Chernogolovka, Russian Academy of Sciences, 142432 Chernogolovka. Translated fromIzvestiya Akademii Nauk, Seriya Khimicheskaya, No. 12, pp. 2755–2759, December, 1992.     

Furan acetal compounds

A method was developed for the preparation of amino derivatives of 1,3-dioxanes of the furan series by amalgam reduction of the corresponding nitro compounds. This method makes it possible to obtain amino compounds without destruction of the furan and dioxane rings. 2--Aminofuryl-5-alkyl-5-methylol- and 5--aminofuryl-5,5-bis(chloromethyl)-1,3-dioxanes and their azomethines were synthesized for the first time.See [5] for communication III.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 4, pp. 440–442, April, 1971.     

Synthesis, structure, and X-band (9.5 GHz) EPR characterization of the new series of pH-sensitive spin probes: N,N-disubstituted 4-amino-2,2,5,5-tetramethyl-3-imidazoline 1-oxyls

[reaction: see text] An approach to the synthesis of new imidazoline nitroxides bearing an N',N'-disubstituted amidine group is reported. The approach is based on the alkylation of diamagnetic 4-R-amino-1,2,2,5,5-pentamethyl-3-imidazolines with bromoacetic acid ethyl ester; the products of alkylation are further oxidized to the corresponding nitroxides. The approach allows a variety of functional groups to be introduced into the nitroxide molecule structure. Alkylation with bromoacetic acid ethyl ester was found to proceed with high regioselectivity and afford the products of exo-alkylation. The regiochemical assignment is made on the basis of 13C NMR spectra and confirmed by X-ray diffraction study. All of the nitroxides synthesized here were shown to have pH-dependent EPR spectra with pKa ranging from 3.5 to 6.2. For nitroxides 13 bearing the carboxylic group remote to the nitroxide moiety, the changes in isotropic magnetic parameters of EPR spectra due to reversible deprotonation of the carboxylic group were found to be small. For these nitroxides, we demonstrate an alternative approach for pKa determination that is based on measuring the peak-to-peak line width of the EPR spectrum in the presence of the paramagnetic broadening agent potassium ferricyanide. The partition coefficients of nitroxides in octanol/H2O and octanol/phosphate buffer solution mixtures were measured to reveal a range of their lipophilicities.     

IR spectra and structure of 2-aryl-3-hydroxypyridines

The IR spectra of methyl, chloro, and phenyl derivatives of 3-hydroxypyridines in CCl₄ solutions and in the crystalline state were studied. A comparison of the frequencies, half widths, and integral intensities of the bands of the stretching vibrations of the hydroxyl groups in the spectra of solutions of the 3-hydroxypyridine derivatives in CCl₄ with the characteristic OH bands in the spectra of phenols demonstrates that 3-hydroxypyridines exist practically completely in the hydroxy form in dilute CCl₄ solutions. The shift in the OH bands in the spectra of 2-phenyl-3-hydroxypyridine derivatives indicates that the OH group forms a -hydrogen bond with the phenyl ring. The presence also of a band of a free OH group is evidence for the existence of s-cis and s-trans conformers relative to the C-O bond.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 2, pp. 187–190, February, 1972.     

Synthesis and tautomeric transformations of 2-(tert-butyl)-1,2,4-benzotriazine-3(2H)-thiones

Treatment of 2-(tert-butyl)-1,2,3,4-benzotetrazinium tetrafluoroborates with sodium thiocyanate afforded 2-(tert-butylazo)phenyl isothiocyanates 3, which exist in equilibrium with 2-(tert-butyl)-1,2,4-benzotriazine-3(2H)-thiones 3′. The equilibrium depends on the substituents R in the benzene ring: the percentage of the open isomer 3 is about 20% for R = H or Me; for R = Cl or Br, the equilibrium is completely shifted to cyclic isomer 3′. The equilibrium is slow on the time scale of the ¹H and ¹³C NMR experiments. For compounds 3a/3′a (R = H), the spectra at 24 °C show two sets of signals, while those at 0 °C contain only signals for isomer 3′a. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1192–1195, July, 2006.