N-tert-Butoxycarbonylation of amines using H3PW12O40 as an efficient heterogeneous and recyclable catalyst

The commercially available heteropoly acid H₃PW₁₂O₄₀ (0.5 mol %) is a very efficient and environmentally benign catalyst for N-tert-butoxycarbonylation of amines (primary, secondary) with di-tert-butyl dicarbonate at room temperature in short reaction times (<10 min). No competitive side products such as isocyanates, ureas, N,N-di-tert-butoxycarbonyls, O-Boc and oxazolidinones were observed. Chiral α-amino alcohols and esters afforded the corresponding N-Boc derivatives chemoselectively in excellent yields.     

Metal-organic chains constructed from pre-organized N2S2 donor ligands

Three new N₂S₂ donor ligands 1,1′-((2-(2-(phenylthio)phenylthio)phenyl)methylene)bis(3,5-R-1H-pyrazole), R = H (L^H), R = Me (L^Me), R = i-Pr (L^i-Pr) have been prepared and characterized. These bifunctional ligands incorporate two distinct chelate donor systems, by virtue of the presence of bispyrazole and bisthioether functions. The preferred conformation of these ligands is such that the N₂ and S₂ donor moieties may be oriented in opposite directions, thus favoring the formation of molecular chains when treated with AgBF₄. The X-ray structures of Ag(I) complexes show that, depending on the steric hindrance present on the pyrazole rings, these ligands behave as κ⁴-SSNN-μ bridging tetradentate (when R = H), or κ³-SNN-μ bridging tridentate (when R = Me, i-Pr). Interestingly, [Ag(L^H)]BF₄ crystallizes in the chiral space group P4₁, with the molecular chain that is folded around the 4₁ screw axis.     

Selective uranyl ion detection by polymeric ion-selective electrodes based on salphenH2 derivatives

The new ion-selective electrodes (ISEs) based on salphenH₂ derivatives such as N,N′-(propylenedioxy)benzenebis(salicylideneimine) L¹ and N,N′-4,5-(propylenedioxy)benzenebis(3,5-di-tert-butylsalicylideneimine) L² as cation carriers are developed for a uranyl ion. The combination of these new ionophores with tris(2-ethylhexyl)phosphate (TEHP) as a plasticizer particularly shows near Nernstian slope in the wide concentration range (1.0 × 10⁻⁶ to 1.0 × 10⁻² M) of UO₂²⁺ and is observed well in the pH range from 1.0 to 5.0 with a response time less than 20 s. Since the employed ionophores were confirmed to form well-defined stable 1:1 complexes with UO₂²⁺, the observed high selectivity for a uranyl ion over the other cations was attributed to the selective complexation as well as the lipophilic behavior of these ligands especially for L². The proposed electrodes offered practically low detection limit of 6.5 × 10⁻⁷ M and reasonably good end-points within experimental error were obtained when the sensor was used as an indicator electrode for the potentiometric titration.     

A convenient method for the Ru(0)-catalyzed regioselective deuteration of N-alkyl-substituted anilines

A highly effective and operationally practical method for the regioselective deuteration of N-alkyl-substituted anilines employing Ru₃(CO)₁₂ (?1 mol %) as catalyst and D₂O as deuterium source was described. A variety of N-alkyl-substituted anilines were efficiently deuterated (up to 98%) at the ortho and/or para position with respect to the nitrogen at neutral conditions. Under the present conditions, deuterated anilines can be easily obtained with simple extraction and evaporation. Substituents with aromatic methoxy groups would not influence the selectivity compared to previous method.     

Synthesis,crystal structure,magnetic property and DNA cleavage activity of a new terephthalate-bridged tetranuclear copper(II) complex

A new terephthalate-bridged tetranuclear copper(II) complex has been synthesized and structurally characterized by X-ray crystallography: [Cu₄(L)₂(tp)(dmf)₂] (1) (H₃L = 1,3-bis(salicylideneamino)propan-2-ol, tp = terephthalate and dmf = N,N′-dimethylformamide). The dinucleating pentadentate character of the ligand (H₃L) and the desired pair-of-dimers arrangement, through the incorporation of the bridging terephthalate moiety, is clearly evident from the structure of 1. The copper atoms are coordinated in a slightly distorted square pyramidal arrangement within each dinucleating half of the complex and are bridged mono-atomically by the secondary alkoxo oxygen of the ligand and di-atomically by the terephthalate moiety. The apical position is occupied by the oxygen atom of the dmf. The structure of 1 reveals a short intramolecular Cu–Cu separation (ca. 3.1 Å), in combination with long intramolecular copper separations (ca. 11 Å). The variable temperature-dependent susceptibility measurement (2–300 K) of 1 reveals a dominant ferromagnetic coupling, 2J = 18.70 cm⁻¹. Complex 1 binds to double-stranded CT (calf-thymus) DNA giving a K_app value of 1.25 × 10⁷ M⁻¹ and displays efficient cleavage of supercoiled pUC19 DNA in the presence of H₂O₂ following a hydroxyl radical pathway.     

Syntheses,crystal structures,and properties of Ni(II) and Co(III) complexes derived from tripod polypyridine ligands containing N7 or N6 donor set atoms

New complexes [Ni^II(pbpaen)](ClO₄)₂ (1) and [Co^III(pbpaen)](ClO₄)₃ (2) (pbpaen = N′-(pyridin-2-ylmethyl)-N,N-bis {2-[(pyridin-2-ylmethyl)amino]ethyl}ethane-1,2-diamine) have been synthesized and characterized by IR and UV–Vis spectroscopies. An X-ray structure of the nickel(II) complex shows that [Ni(pbpaen)](ClO₄)₂ (1) crystallizes in the monoclinic space group P2_1/c. The cation [Ni(pbpaen)]²⁺ is pseudo-octahedral with one of the three pyridyl nitrogen atom uncoordinated. The crystal lattice of this complex is stabilized by intra and intermolecular hydrogen bonding systems, giving one-dimensional sheets like arrays. All attempts to obtain nickel or cobalt complexes with protonated forms of the ligand resulted in isolation of only [Co^III(bpaen)](ClO₄)₃ (3) compound in which the tripod pbpaen ligand has lost one of the three pyridylmethyl groups, procuring then bpaen ligand {bpaen = N,N-bis{2-[(pyridin-2-ylmethyl)amino]ethyl}ethane-1,2-diamine}. The X-ray crystal structure reveals that the compound 3 crystallizes in the orthorhombic space group Pna2 with the Co³⁺ ion having a distorted-octahedral environment. These two ligands with strong-field N donor stabilise the +3 oxidation state of the Co center.     

Synthesis,structure, and electrochemistry of pyridinecarboxamide cobalt(III) complexes; the effect of bridge substituents on the redox properties

Two series of complexes of the types trans-[Co^III(Mebpb)(amine)₂]ClO₄ {Mebpb²⁻ = N,N-bis(pyridine-2-carboxamido)-4-methylbenzene dianion, and amine = pyrrolidine (prldn) (1a), piperidine (pprdn) (2a), morpholine (mrpln) (3a), benzylamine (bzlan) (4a)}, and trans-[Co^III(cbpb)(amine)₂]X {cbpb²⁻ = N,N-bis(pyridine-2-carboxamido)-4-chlorobenzene dianion, and amine = pyrrolidine (prldn), X = PF₆ (1b), piperidine (pprdn), X = PF₆ (2b), morpholine (mrpln), X = ClO₄ (3b), benzylamine (bzlan), X = PF₆ (4b)} have been synthesized and characterized by elemental analyses, IR, UV–Vis, and ¹H NMR spectroscopy. The crystal structure of 1a has been determined by X-ray diffraction. The electrochemical behavior of these complexes, with the goal of evaluating the effect of axial ligation and equatorial substitution on the redox properties, is also reported. The reduction potential of Co^III, ranging from −0.53 V for (1a) to −0.31 V for (3a) and from −0.48 V for (1b) to −0.22 V for (3b) show a relatively good correlation with the σ-donor ability of the axial ligands. The methyl and chloro substituents of the equatorial ligand have a considerable effect on the redox potentials of the central cobalt ion and the ligand-centered redox processes.     

Synthesis and structural characterization of Al7C3N3-homeotypic aluminum silicon oxycarbonitride, (Al7−xSix)(OyCzN6−y−z) (x∼1.2, y∼1.0 and z∼3.5)

A new aluminum silicon oxycarbonitride, (Al_5.8Si_1.2)(O_1.0C_3.5N_1.5), has been synthesized and characterized by X-ray powder diffraction (XRPD), transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDX) and electron energy loss spectroscopy (EELS). The title compound is hexagonal with space group P6₃/mmc and unit-cell dimensions a=0.322508(4) nm, c=3.17193(4) nm and V=0.285717(6) nm³. The atom ratios of Al:Si and those of O:C:N were, respectively, determined by EDX and EELS. The initial structural model was successfully derived from the XRPD data by the direct methods and further refined by the Rietveld method. The crystal is most probably composed of four types of domains with nearly the same fraction, each of which is isotypic to Al₇C₃N₃ with space group P6₃mc. The existence of another new oxycarbonitride (Al_6.6Si_1.4)(O_0.7C_4.3N_2.0), which must be homeotypic to Al₈C₃N₄, has been also demonstrated by XRPD and TEM.     

Aqua bridged Cu2 dimer of a heptadentate N4O3 coordinating ligand: Synthesis,structure and magnetic properties

The N₄O₃ coordinating heptadentate imidazolidinyl phenolate ligand, H₃L (2-(2′-hydroxyphenyl)-1,3-bis[4-(2-hydroxyphenyl)-3-azabut-3-enyl]-1,3-imidazolidine) forms with Cu(II) a rare aqua bridged complex [{Cu₂(μ-L)(μ-H₂O)}₂](ClO₄)₂ · 4.5H₂O (1 · 4.5H₂O). Complex 1 · 4.5H₂O contains two crystallographically different but chemically equivalent dinuclear [Cu₂(μ-L)(μ-H₂O)]⁺ cationic units in the asymmetric unit. The copper atoms of each dinuclear unit are in a distorted square-pyramidal environment and are held together by phenolate, imidazolidinyl and aqua bridges with a Cu···Cu separation of av. 3.34 Å. The compound exhibits a very weak antiferromagnetic exchange interaction (J = −0.77 cm⁻¹, ? = −2 J?₁?₂) between the two copper(II) (S = 1/2) ions. The ¹H NMR spectrum of the complex shows a total of 17 hyperfine shifted peaks, as expected from the idealized C_s symmetry of the compound, spread over a very large window of chemical shift, spanning about 250 ppm. The complex, having an appropriate intermetallic separation for catechol binding, shows catecholase like activity in MeCN at 25 °C, with the aerobic oxidation of 3,5-di-tert-butylcatechol (3,5-DTBC) to 3,5-di-tert-butylquinone (3,5-DTBQ).     

Hydrothermal synthesis, characterization, and photocatalytic properties of Zn2SnO4

Nanosized Zn₂SnO₄ (ZTO) particles were successfully synthesized by a simple hydrothermal process in water/ethylene glycol mixed solution using amines (ethylamine, n-butylamine, n-hexylamine, and n-octylamine) as mineralizer. The products were characterized by X-ray diffractions (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and N₂ adsorption. The results indicated that the hydrothermal conditions, such as alkaline concentration (n-butylamine), reaction temperature, solvent composition, and the kind of amines, had an important influence on the composition, crystallinity, and morphology of the product. The as-synthesized ZTO samples exhibited high activities and durabilities for photodegradation of methyl orange and the activities were mainly affected by the crystallinities of the samples. A hexagonal-shaped ZTO (H-ZTO) sample was prepared in 0.53 M of n-butylamine solution at 180 °C for 20 h and its optical properties were characterized by UV-Vis diffuse reflectance and Photoluminescence (PL) spectra. Furthermore, the photocatalytic H₂ evolution reaction from ethanol aqueous solution over H-ZTO was also investigated.     

An antiferromagnetically coupled hexanuclear copper(II) Schiff base complex containing phenoxo and dicyanamido bridges: Structural aspects and magnetic properties

A novel hexanuclear complex [{(CuL)₂Cu}₂(μ-dca)₂](ClO₄)₂·2L′(1) (where H₂L = (OH)C₆H₄C(CH₃)N(CH₂)₃NC(CH₃)C₆H₄(OH) or N,N′-bis(2-hydroxyacetophenone) propylenediimine and dca = N(CN)₂⁻ and L′ = 2-hydroxyacetophenone) has been synthesized and characterized by elemental analysis, UV-Vis, FT-IR spectroscopic and electrochemical methods. Single crystal X-ray structural characterization reveals a centrosymmetric nature of the complex unit, where the metal centers adopt distorted square-planar and distorted octahedral geometries. Structural analysis also reveals μ₂-phenoxo bridges between terminal and the central copper(II) centers of the asymmetric [(CuL)₂Cu(dca)] unit, the latter being interconnected to its symmetry related counterpart by double μ_1,5-dca bridges, leading to the hexanuclear complex ion [{(CuL)₂Cu}₂(μ-dca)₂]²⁺. Low temperature susceptibility measurements of 1 revealed the presence of strong antiferromagnetic coupling (2J = −407 cm⁻¹) between the copper(II) centers.     

Synthesis, structure, and magnetism of Tb4PdGa12 and Tb4PtGa12

Single crystals of Tb₄MGa₁₂ (M=Pd, Pt) have been synthesized. The isostructural compounds crystallize in the cubic space group , with Z=2 and lattice parameters: a=8.5940(5) and 8.5850(3) Å for Tb₄PdGa₁₂ and Tb₄PtGa₁₂, respectively. The crystal structure consists of corner-sharing MGa₆ octahedra and TbGa₃ cuboctahedra. Magnetic measurements suggest that Tb₄PdGa₁₂ is an antiferromagnetic metamagnet with a Néel temperature of 16 K, while the Pt analog orders at T_N=12 K.     

Crystal structures and magnetic properties of CeAu4Si2 and CeAu2Si2

Single crystals of CeAu₄Si₂ and CeAu₂Si₂ have been grown out of ternary fluxes rich in Au, and the former, also by sintering the stoichiometric composition at 750 °C. The single-crystal X-ray refinement result for CeAu₄Si₂ is orthorhombic, Cmmm (No. 65, Z=2), different from a tetragonal result found from an X-ray powder diffraction refinement [H. Nakashima, et al., J. Alloys Compds. 424 (2006) 7]. For CeAu₂Si₂, this is the first report of the stoichiometric crystalline phase, in the known tetragonal I4/mmm structure. The anisotropic field- and temperature-dependent magnetizations, as well as specific heat and resistivity data are compared. Although both compounds have related structural packing, they present unique magnetic features. CeAu₂Si₂ is a typical antiferromagnet with T_N=8.8(1) K and CeAu₄Si₂ features a ferromagnetic component below T_c=3.3(1) K. Both phases have effective moments close in value to that of free Ce³⁺.     

Structure and magnetic properties of the cubic oxide fluoride BaFeO2F

Fluorination of the parent oxide, BaFeO_3−δ, with polyvinylidine fluoride gives rise to a cubic compound with a=4.0603(4) Å at 298 K. ⁵⁷Fe Mössbauer spectra confirmed that all the iron is present as Fe³⁺. Neutron diffraction data showed complete occupancy of the anion sites, indicating a composition BaFeO₂F, with a large displacement of the iron off-site. The magnetic ordering temperature was determined as T_N=645±5 K. Neutron diffraction data at 4.2 K established G-type antiferromagnetism with a magnetic moment per Fe³⁺ ion of 3.95 μ_B. However, magnetisation measurements indicated the presence of a weak ferromagnetic moment that is assigned to the canting of the antiferromagnetic structure. ⁵⁷Fe Mössbauer spectra in the temperature range 10-300 K were fitted with a model of fluoride ion distribution that retains charge neutrality of the perovskite unit cell.     

Aminotroponiminate alkyl and alkoxide complexes of zinc

Reaction of {(iPr)₂ATI} H((iPr)₂ATI = N-isopropyl-2-(isopropylamino)troponiminate) with dimethyl zinc in toluene afforded the methyl complex [{(iPr)₂ATI}Zn-Me]. Subsequent reaction of [{(iPr)₂ATI}Zn-Me] with different alcohols gave the alkoxide complexes [{(iPr)₂ATI}Zn-OR]₂ (R = iPr, tBu, Ph). These compounds, which were investigated by single crystal X-ray diffraction, are dimeric in the solid-state. In the solid-state the metal centers are bridged symmetrically by two μ-oxygen atoms, thus a flat Zn-O-Zn′-O′ plane is observed. [{(iPr)₂ATI}Zn-OR]₂ were used as catalysts for the copolymerization experiments of epoxides and CO₂.     

Amorphous and nanocrystalline titanium nitride and carbonitride materials obtained by solution phase ammonolysis of Ti(NMe2)4

Solution phase reactions between tetrakisdimethylamidotitanium (Ti(NMe₂)₄) and ammonia yield precipitates with composition TiC_0.5N_1.1H_2.3. Thermogravimetric analysis (TGA) indicates that decomposition of these precursor materials proceeds in two steps to yield rocksalt-structured TiN or Ti(C,N), depending upon the gas atmosphere. Heating to above 700 °C in NH₃ yields nearly stoichiometric TiN. However, heating in N₂ atmosphere leads to isostructural carbonitrides, approximately TiC_0.2N_0.8 in composition. The particle sizes of these materials range between 4-12 nm. Heating to a temperature that corresponds to the intermediate plateau in the TGA curve (450 °C) results in a black powder that is X-ray amorphous and is electrically conducting. The bulk chemical composition of this material is found to be TiC_0.22N_1.01H_0.07, or Ti₃(C_0.17N_0.78H_0.05)_3.96, close to Ti₃(C,N)₄. Previous workers have suggested that the intermediate compound was an amorphous form of Ti₃N₄. TEM investigation of the material indicates the presence of nanocrystalline regions <5 nm in dimension embedded in an amorphous matrix. Raman and IR reflectance data indicate some structural similarity with the rocksalt-structured TiN and Ti(C,N) phases, but with disorder and substantial vacancies or other defects. XAS indicates that the local structure of the amorphous solid is based on the rocksalt structure, but with a large proportion of vacancies on both the cation (Ti) and anion (C,N) sites. The first shell Ti coordination is approximately 4.5 and the second-shell coordination ∼5.5 compared with expected values of 6 and 12, respectively, for the ideal rocksalt structure. The material is thus approximately 50% less dense than known Ti_x(C,N)_y crystalline phases.     

Copper-catalyzed cross-coupling of sulfonamides with aryl iodides and bromides facilitated by amino acid ligands

A highly general, convenient, and inexpensive catalyst system was developed for the N-arylation of sulfonamides with aryl iodides or bromides by using 5-20 mol % of CuI as catalyst, 20 mol % of N-methylglycine (for aryl iodides) or N,N-dimethylglycine (for aryl bromides) as ligand, and K₃PO₄ as base.     

Singlet-triplet energy separations in divalent five-membered cyclic conjugated C5H3X, C4H3SiX, C4H3GeX, C4H3SnX, and C4H3PbX (X = H, F, Cl, and Br)

Singlet-triplet energy gaps in cyclopenta-2,4-dienylidene, as well as its 2- or 3-halogenated derivatives, are compared and contrasted with their sila, germa, stana, and plumba analogues; at HF/6-31G* and B3LYP/ 6-311++G(3df, 2p) levels of theory. Energy gaps (ΔG_t-s), between triplet (t) and singlet (s) states, appear linearly proportional to: (i) the size of the group 14 divalent element (M = C, Si, Ge, Sn and Pb), (ii) the angle ∠C-M-C, and (iii) the ΔG_(LUMO-HOMO) of the singlet state involved. The magnitude of ΔG_t-s, for each 2- and/or 3-substituted species studied, increases with an order of: carbenes < silylenes < germylenes < stanylenes < plumbylenes. This order reverses for the barriers of the ring puckering. The puckering occurs with more ease for every singlet, compared to its corresponding triplet form.Regardless of the group 14 element (M) employed, every 3-halo-substituted species is more stable than the corresponding 2-halo-substituted isomer. For M = Pb, Sn and/or Ge; 3-halo-substituted species have higher ΔG_t-s than their corresponding 2-halo-substituted analogues. For M = Si, similar ΔG_t-s are found for 2- and 3-halogenated isomers. For M = C, 3-halo-substituted species have lower ΔG_t-s than their corresponding 2-halo-substituted analogues.Every cyclic singlet has a larger ∠C-M-C angle, than its corresponding cyclic triplet state, except for 3-halosilacyclopenta-2,4-dienylidenes where triplet has a larger ∠C-M-C angle than its corresponding singlet state.     

Synthesis, characterization and X-ray crystal structures of seven-coordinate pentagonal-bipyramidal zinc(II), cadmium(II) and tin(IV) complexes of a pentadentate N3S2 thiosemicarbazone

New complexes of the general formula, [M(H₂dap⁴NMetsc)(H₂O)₂](NO₃)₂·H₂O (M = Zn²⁺, Cd²⁺; H₂dap⁴NMetsc = 2,6-diacetylpyridinebis(⁴N-methylthiosemicarbazone) and [Sn((dap⁴NMetsc)X₂] (X = Ph, Cl and I) (dap⁴NMetsc = the doubly deprotonated form of 2,6-diacetylpyridine bis(⁴N-methylthiosemicarbazone) have been synthesized and structurally characterized by a variety of physico-chemical techniques. X-ray crystallographic structure determination shows that in the zinc and cadmium complexes, the bis(thiosemicarbazone) ligand coordinates as a neutral N₃S₂ pentadentate chelating agent through the two azomethine nitrogen atoms, the pyridine nitrogen atom and the two thione sulfur atoms. The N₃S₂ donors of the ligand occupy the equatorial plane and the two aqua ligands occupy the sixth and seventh axial positions of the seven-coordinated cadmium(II) and zinc(II) ions. In the tin(IV) complexes, however, the thiosemicarbazone is coordinated to the tin(IV) ion as a dinegatively charged pentadentate chelating agent via the pyridine nitrogen atom, the two azomethine nitrogen atoms and the two thiolate sulfur atoms. The two apical positions of the seven-coordinate tin(IV) ion are occupied by either phenyl, chlorido or iodido ligands. In each of the complexes, the overall geometry adopted by the metal ion may be considered as a distorted pentagonal-bipyramid.