Theoretical modeling of the mechanism of aniline oxidation by singlet O<Subscript>2</Subscript>

The mechanism of aniline oxidation by singlet oxygen was studied by the DFT-PBE/L2 method. According to the calculations, aniline endoperoxide cannot participate in the reaction because of its energy instability. The addition of ¹O₂ to aniline proceeds with the simultaneous proton transfer to the oxygen molecule from the NH₂ group (for the syn-approach of oxygen) or from the aromatic ring (for the anti-approach). For the syn-approach of the ¹O₂ molecule, the HNC₆H₄(H)OOH intermediate is formed, whose decomposition leads to aniline p-hydroperoxide (predominantly) or p-iminoquinone. In the case of the anti-approach, the ¹O₂ molecule is inserted at the C–H bond to form aniline p-hydroperoxide (H₂NC₆H₄OOH). The decomposition of aniline p-hydroperoxide with the formation of p-aminophenol and H₂O₂ molecule proceeds via concerted mechanism.     

Reactions of acetylene ketones in superacids

Vinyl type cations ArC⁺=CHCOR generated from acetylene ketones ArC≡CCOR in superacids HSO₃F and CF₃SO₃H react with diverse benzene derivatives to form alkenylation products, E-/Z-isomers of diarylpropenone structures Ar(Ar’)C=CHCOR. The alkenylation of aromatic compounds with acetylene ketones in superacids occurs with the primary syn-addition of a hydrogen and an aryl residue to the acetylene bond followed by transformation of the product into anti-isomer under the conditions of the reaction.     

Zur Strukturaufklärung der Isomeren von α-Oximinocarbonsäureestern

The theoretical and experimental dipole moments for a number ofsyn- andanti-α-oximino esters are determined.NMR- andIR-spectra are reported. On the basis of these and previous chemical investigations the preferred steric structures of thesyn- andanti-forms are ascertained. Two rotational isomers exist in the same degree with thesyn-forms. Due to resonance effects and hydrogen bonds they are relatively stable.     

Electronic structure and energy decomposition of binuclear transition metal complexes containing β-diketiminate and imido ligands: spin state and metal’s nature effects

DFT calculations with full geometry optimization using BP86-D and OPBE functionals have been performed on series of [(BDI)M(NH)]₂(Bz) and [(BDI)M(NH)]₂(Tol) (M = Ti, V, Nb, Cr, Mn, Fe, Co, and Ni; BDI = β-diketiminate; NH = imido group; Bz = benzene; and Tol = toluene) of various spin states (singlet S = 0, triplet S = 1, quintet S = 2, and singlet S = 0 of broken symmetry method). Depending on the metal nature and its electron count and the spin state, the six-membered ring in [(BDI)M(NH)]₂(Bz) and [(BDI)M(NH)]₂(Tol) adopts various hapticities that involve full or partial coordination, giving rise to a flat or a distorted ring, respectively. The NH^2? imido group is linear or bent with respect to its sp or sp² hybridization acting as a six- or a four-electron donor, respectively. The (BDI)^? anion is a bidentate ligand as a six-electron donor. The optimized geometries do not show direct metal-metal bonding and correspond to long separations. The optimized structures for Nb metal are comparable to the available experimental ones. The Ziegler-Rauk energy decomposition analysis scheme was employed to characterize the geometry distortion, the steric interaction (electrostatic and Pauli), and the orbital interaction terms in the total bonding energy. The results showed that the interaction terms in all the studied complexes are governed by one third covalent and two thirds ionic characters, which are in agreement with the ΔE_elstat (electrostatic) and ΔE_orb (orbital) contributions, respectively, into the total attractive interaction (ΔE_elstat + ΔE_orb).     

Stereoselectivity of halomethoxylation of 1-phenyltricyclo-[4.1.0.0<Superscript>2,7</Superscript>]heptane and methyl 7-phenyltricyclo[4.1.0.0<Superscript>2,7</Superscript>]-heptane-1-carboxylate

The stereoselectivity of halomethoxylation of 1-phenyltricyclo[4.1.0.0^2,7]heptane and methyl 7-phenyltricyclo[4.1.0.0^2,7]heptane-1-carboxylate at the central bicyclobutane C¹-C⁷ bond by the action of N-chloro-, N-bromo-, and N-iodosuccinimides in methanol depends on the halogen nature. Conjugate chlorination and bromination are characterized by pronounced anti-stereoselectivity; the contribution of syn-addition slightly increases in going from the monosubstituted tricycloheptane substrate to disubstituted. Iodomethoxylation of the latter is clearly syn-stereoselective.     

Conjugate halo- and mercuroazidation of 1-phenyltricyclo-[4.1.0.0<Superscript>2.7</Superscript>]heptane. Synthesis of a conformationally rigid α-amino acid with a bicyclo[3.1.1]heptane skeleton

1-Phenyltricyclo[4.1.0.0^2.7]heptane reacted with N-bromo-, N-chloro-, and N-iodosuccinimides and with mercury(II) acetate in the presence of sodium azide as external nucleophile to give conjugate addition products to the central C¹–C⁷ bicyclobutane bond with a norpinane structure, where the azido group and the phenyl were attached to the same carbon atom (C⁶). The bromo- and chloroazidation showed anti-stereo-selectivity, and the iodoazidation, moderate syn-stereoselectivity; the mercuroazidation afforded exclusively the corresponding syn-addition product. Hydro-, bromo- and chlorodemercuration of the mercury adduct with sodium tetrahydridoborate and elemental bromine and chlorine, respectively, did not involve the azido group, and the original configuration was retained. The reduction of the hydrodemercuration product with LiAlH₄ gave 6-exo-phenylbicyclo[3.1.1]heptan-6-amine which was transformed in three steps into conformationally rigid 6-endo-(acetamido)bicyclo[3.1.1]heptane-6-carboxylic acid.     

Atropisomeric <Emphasis Type="Italic">N</Emphasis>-acyl-<Emphasis Type="Italic">N</Emphasis>-(cyclopentenylphenyl)glycines in the synthesis of oxazolo[3,4-<Emphasis Type="Italic">a</Emphasis>]benzoxazocinones

Intramolecular [3+2]-cycloaddition was studied of munchnones generated at heating syn- and anti-atropisomers of N-acyl-N-[6-methyl-2-(cyclopent-2-en-1-yl)phenyl]glycines with acetic anhydride. By spectral and X-ray diffraction analysis syn-isomers of acids and tetrahydro-1,4,7-methanetriyl[1,3]oxazolo[3,4-a][1]- bensazocin-3(3aH)-ones were identified.     

Halogenation of <Emphasis Type="Italic">N</Emphasis>-substituted <Emphasis Type="Italic">p</Emphasis>-quinone monoimines and <Emphasis Type="Italic">p</Emphasis>-quinone monooxime ethers: XV. Synthesis and bromination of 4-(cinnamoyloxyimino)-cyclohexa-2,5-dienones

New 4-(cinnamoyloxyimino)cyclohexa-2,5-dien-1-ones were synthesized, and their bromination afforded bromine addition products to the syn- and anti-C=C bonds of the quinoid ring. In all cases, bromine addition to the C=C double bond of the cinnamoyl fragment was observed.     

Synthesis of 7-sulfonyl-substituted norpinan-6-ones and -thiones from 1-bromotricyclo[4.1.0.0<Superscript>2,7</Superscript>]heptane

1-Bromotricyclo[4.1.0.0^2,7]heptane reacted with benzene- and methanesulfonyl thiocyanates in benzene at 20°C via anti addition to the central C¹–C⁷ bicyclobutane bond with formation of 6-endo-bromo-6-exo-thiocyanato-7-syn-(R-sulfonyl)bicyclo[3.1.1]heptanes. Treatment of the benzenesulfonyl thiocyanate adduct with potassium tert-butoxide in THF at 20°C gave 7-endo-(benzenesulfonyl)norpinan-6-one, whereas the reaction with 1,8-diazabicyclo[5.4.0]undec-7-ene in methylene chloride afforded 7-exo-(benzenesulfonyl)-norpinane-6-thione which was converted into 7-exo-(benzenesulfonyl)norpinan-6-one by alkaline hydrolysis.     

Aromaticity of Bare Iridium Trimers and Ir3M0/+ and $$\rm{Ir}_3M_2^{+/3+}$$ (M = Li,Na, K,and Be,Ca) Bimetallic Clusters

The structural stabilities, bonding nature, electronic properties, and aromaticity of bare iridium trimers \(\rm{Ir}_3^{+/-}\) with different geometries and spin multiplicities are studied at the DFT/B3LYP level of theory. The ground state of the \(\rm{Ir}_3^{+}\) cation is found to be the ³A₂ (C_2v) triplet state and the ground state of the \(\rm{Ir}_3^{-}\) anion the ⁵A₂ (C_2v) quintet state. A detailed molecular orbital (MO) analysis indicates that the ground-state \(\rm{Ir}_3^{+}\) ion (C_2v, ³A₂) possesses double (σ and partial δ) aromaticity as well as the ground-state \(\rm{Ir}_3^{-}\) ion (C_2v, ⁵A₂). The multiple d-orbital aromaticity is responsible for the totally delocalized three-center metal-metal bond of the triangular Ir₃ framework. \(\rm{Ir}_3^{-}\) (C_2v, ¹A₁) structure motif is perfectly preserved in pyramidal Ir₃M^0/+ (C_s, ¹A′) and bipyramidal \(\rm{Ir}_3M_2^{+/3+}\) (C_2v, ¹A₁) (M = Li, Na, K and Be, Ca) bimetallic clusters which also possess the corresponding d-orbital aromatic characters.     

Structure of methyl-7-methoxy-7-phenyl-6-<Emphasis Type="Italic">endo</Emphasis>-halobicyclo[3.1.1]heptane-6-<Emphasis Type="Italic">exo</Emphasis>-carboxylate diastereomers in single crystals

The structure of diastereomeric methyl-7-anti-methoxy-7-syn-phenyl-and methyl-7-syn-methoxy-7-anti-phenyl-6-endo-bromobicyclo[3.1.1]heptane-6-exo-carboxylates 2a and 3a and their chlorine-and iodine-substituted analogs 2b and 3c was studied by XRD. The diastereomers differ in the geometrical parameters of the carbon framework of the molecules. The C(1)-C(2)-C(3)-C(4)-C(5)-C(6) six-membered ring is in the intermediate conformation between envelope and chair in structures 2 and envelope in structures 3. In compound 2a, the cyclobutane fragment has a higher degree of folding than in 3a; one of the possible reasons for that is the donor-acceptor interaction between the 6-methoxycarboxylic and 7-methoxy groups in molecule 2a.     

Hydrogenolysis of 7-phenyltricyclo[4.1.0.0<Superscript>2,7</Superscript>]heptan-1-carboxylic acid. Synthesis of ketones with tricyclo[4.4.0.0<Superscript>2,7</Superscript>]decane and tricyclo[5.4.0.0<Superscript>2,8</Superscript>]undecane skeletons

Hydrogenation of 7-phenyltricyclo[4.1.0.0^2,7]heptane-1-carboxylic acid over Raney nickel occurred in the syn-stereoselective fashion to give anti-7-phenylbicyclo[3.1.1]heptane-exo-6-carboxylic acid. The latter was used to synthesize 4,5-benzotricyclo[4.4.0.0^2,7]dec-4-en-3-one and two isomeric higher homologs, 5,6-benzotricyclo[5.4.0.0^2,8]undec-5-en-3-and-4-ones.     

Switching diastereoselectivity of direct Mannich-type reaction of cyclic ketones by polymeric laponite nanoclay catalyst

A new polymeric laponite nanoclay heterogeneous catalytic system based on HPMC (hydroxypropyl methyl cellulose) was developed for direct Mannich-type reaction of ketones with substituted benzaldehydes and anilines to afford corresponding β-amino ketones in good to high yields. Interestingly, cyclic ketones exhibited different chemoselectivity. Cyclopentanone underwent aldol condensation to give crossed-aldol product, while cyclohexanone and cyclopentanone afforded corresponding Mannich adducts. In the case of cyclohexanone, stereoselectivity was changed depending on the nature of the substitution on benzaldehydes, in which, moderate electron-donating and electron-withdrawing groups afforded the anti isomer as major products, but strongly electron-donating substituted benzaldehydes led to syn isomer as the major Mannich adducts. Mannich reaction with cycloheptanone led to Mannich adducts with excellent syn selectivity.     

EPR studies of covalent bonding and hyperfine coupling in the complexes of <Emphasis Type="Italic">ns</Emphasis><Superscript>1</Superscript> ions

Covalent bonding in the complexes containing ns ¹ ions of various metals was studied by EPR spectroscopy. Large series of octahedral, cubic, and cuboctahedral complexes of the ⁶⁷Zn⁺(4s ¹), ¹¹¹Cd⁺(5s ¹), ²⁰⁵Tl²⁺(6s ¹), and ²⁰⁷Pb³⁺(6s ¹) ions were analyzed in crystal structures like fluoroperovskite (KMgF₃), fluoroantiperovskite (LiBaF₃), fluorite (MF₂) (where M = Ca, Sr, and Ba), and alkali metal halides. The parameters of hyperfine couplings and ligand hyperfine couplings were interpreted with regard to bond covalence and spin polarization.     

New coordination modes of iminodiacetamide type ligands in palladium(II) complexes: crystallographic and DFT studies

The reactions of N-alkyliminodiacetamide derivatives, namely N-ethyliminodiacetamide (CH₃CH₂N(CH₂CONH₂)₂; Etimda) and N-isopropyliminodiacetamide (CH₃)₂CHN(CH₂CONH₂)₂; i-Primda), with sodium tetrachloropalladate(II) in aqueous solutions were investigated. Three new palladium(II) complexes, [Pd(Etimda_?H)₂]?2H₂O (1), [Pd(i-Primda_?H)₂]?2H₂O (2) and [PdCl₂(i-Primda)] (3), were obtained and characterized by X-ray structural analysis, infrared spectroscopy and thermal analysis (TGA). The square planar coordination environments around the palladium(II) ions in complexes 1 and 2 consist of two N,N′-bidentate N-alkyliminodiacetamidato ligands, with imino N atoms in trans-position. The complex 3 also exhibits a square planar coordination environment around Pd(II), but with two chloride ions and one neutral N-isopropyliminodiacetamide ligand bound in an N,O′-bidentate coordination mode. The described coordination modes, as well as the presence of deprotonated amide groups in ligands in 1 and 2, are found for the first time in palladium(II) complexes with iminodiacetamide type ligands. The molecular geometries and infrared spectra of these three complexes were also modelled using DFT calculations, at the BP86-D3/def2-TZVPP/PCM level of theory. The RMSD values suggest a good agreement of the calculated and experimental geometries. A QTAIM analysis suggests a qualitative correlation between bond lengths and energy densities, also supported by an NBO analysis. The dimer interaction energy between complex units was estimated at about ?15 kcal/mol for all complexes.     

Synthesis and Characterization of Archetypal Ladder-Like Dibutyloxotin Cluster Derived from Sterically Encumbered 4-[(<Emphasis Type="Italic">E</Emphasis>)-2-(4-hydroxy-5-methylphenyl)-1-diazenyl]benzoate

Reaction of Bu₂SnO with 4-[(E)-2-(4-hydroxy-5-methylphenyl)-1-diazenyl]benzoic acid in toluene yielded a tetranuclear tin cluster {[Bu₂Sn(O₂CC₆H₄(N=N(C₆H₃-4-OH-5-CH₃))-p)]₂O}₂·2EtOH (1). The complex 1 was characterized using IR spectroscopy, NMR, elemental analysis and single-crystal X-ray diffraction. The compound is a centrosymmetric tetranuclear bis(dicarboxylatotetrabutyldistannoxane) complex containing a planar Sn₄O₂ core in which two μ ₃-oxo O-atoms connect an Sn₂O₂ ring to two exocyclic Sn-atoms. The four carboxylate ligands display two different modes of coordination: syn–syn O, O′-bridging and mono atomic bridge. In the complex, the geometry around the tin atoms is distorted trigonal bipyramidal with an additional longer Sn···O contact.     

XPS spectra of free nitroxyl radicals and their electronic structure

The N(1s) and O(1s) XPS spectra of stable nitroxyl radicals and molecules with a related heterocycle structure: 4,4,5,5-tetramethyl-2-phenyl-4,5-dihydro-1H-imidazole-3-oxide-1-oxyl, 4,4,5,5-tetramethyl-2-(3-nitrophenyl)-4,5-dihydro-1H-imidazole-3-oxide-1-oxyl, 4,4,5,5-tetramethyl-2-(2-hydroxyphenyl)-4,5-dihydro-1H-imidazole-3-oxide-1-oxyl, 4,4,5,5-tetramethyl-2-(2-hydroxy-3-nitrophenyl)-4,5-dihydro-1Himidazole-3-oxide-1-oxyl, and 4,4,5,5-tetramethyl-2-phenyl-4,5-dihydro-1H-imidazole-3-oxide were studied. The possibility to apply X-ray electron spectra for investigation of the charge electron and spin density distribution on free radical atoms and at their coordination by a metal is considered.     

Atmospheric levels and distribution of Dechlorane Plus in an E-waste dismantling region of East China

Atmospheric concentrations of Dechlorane Plus(DP)were investigated in Taizhou,an electronic-waste(E-waste)dismantling region in East China.Passive air samplers with polyurethane foam(PUF)disks were deployed every three months during the sampling period of September 2009-August 2010.The total DP(syn-and anti-DP)concentrations in air ranged from not detected to 277 pg/m~3,with a mean concentration of 53.9 pg/m~3.A generally declining trend of DP levels was found from the E-waste dismantling region to the peripheral areas.The median values of total DP concentrations in autumn,winter,spring and summer were 52.2,28.8,39.7 and 30.1 pg/m~3,respectively.The seasonal variations of DP concentrations were mainly associated with the intensity of E-waste dismantling activities and meteorological conditions.The mean value of anti-DP fractional abundance(f_(anti))was 0.74±0.08,which was consistent with those in the commercial DP products.This study confirmed a significant emission source related to the distribution of atmospheric DP in the E-waste dismantling area and supplied information for the seasonal variation of DP in the atmosphere.     

Structural,Electronic and Tunable Magnetic Properties of Transition Metal Doped Rh<Subscript>8</Subscript> Cluster from First Principles Calculation

The configurations, electronic and magnetic properties of the Rh₇M (M?=?3d, 4d transition metal) are systematically investigated within the framework of the generalized gradient approximation density-functional theory (DFT-GGA). The results indicated that the ground state structures of Rh₇M (M?=?3d) clusters prefer to a bicapped octahedron configuration, while the Rh₇M (M?=?4d) clusters present a different degree of geometry reconstruction relative to the perfect cubic structure of Rh₈ cluster. In most cases, the doped clusters show relatively higher stability, indicating that impurity atoms could stabilize the pure Rh₈ cluster; the Rh₇M (M?=?3d, 4d) have smaller frontier orbital energy gaps in comparison to the host. The magnetic moments of Rh₇M (M?=?3d, 4d) exhibit a tunable magnetism with range from 3μ_B to 13μ_B and the Fe atom doping enhances the magnetic moment of mixed cluster.     

Conformations and properties of <Emphasis Type="Italic">O</Emphasis>-Alkyl-<Emphasis Type="Italic">S</Emphasis>-(2-<Emphasis Type="Italic">N</Emphasis>,<Emphasis Type="Italic">N</Emphasis>-dialkylamino)-ethylmethylthiophosphonates

Conformers of the biologically active compounds CH₃P(O)(OR)(SCH₂CH₂NR ₂ ^′ ), where (I) R = i-C₄H₉, R′ = C₂H₅ and (II) R = C₂H₅, R′ = i-C₃H₇, are calculated within the AM1 level of theory. The elongated and twisted forms with maximum and minimum distances between a nitrogen atom and those of a phosphorus tetrahedron, respectively, and bearing a syn and anti oriented alkoxy group relative to a phosphoryl oxygen, are studied. It is found that the differences between the energy, electronic, and geometric parameters of these forms are apparent in differences between their properties, e.g., the ability to participate in complexation and protonation, reactions that to some extent simulate the interaction between a substance and a biological object.