Covalent Bonding in Au(BO) 2 − and Au(BS) 2 −

We perform in this work a comprehensive first-principles investigation on the geometric and electronic structures of Au(BO) ₂ ^? and Au(BS) ₂ ^? which are valent isoelectronic to the well-known Au(CN) ₂ ^? monoanion. Au(BO) ₂ ^? and Au(BS) ₂ ^? complexes prove to possess linear ground-state structures similar to Au(CN) ₂ ^? and the BO^? and BS^? ligands in them are found to be coordinated terminally via boron atoms to gold centers which are weakly negatively charged. Au–B bonds in Au(BO) ₂ ^? and Au(BS) ₂ ^? appear to have higher Wiberg bond indices (0.79 and 0.80) and more covalent components (60 and 53 %) than the corresponding values of Au–C interaction in Au(CN) ₂ ^? (0.67 and 39 %, respectively) at the same theoretical levels. Their Au–B bifurcation values of the electronic localization function also turn out to be higher than Au–C. These results strongly suggest that the Au–B bonds in Au(BO) ₂ ^? and Au(BS) ₂ ^? with multiple-bond character possess stronger covalent characters than Au–C in Au(CN) ₂ ^? .     

Synthesis,Characterization and Crystal Structure of (PhCH2)2Sn(S2CENt2) and (PhCH2)2Sn(S2CNC4H8)2

Two new dibenzyltin bisditiocarbamates(PhCH2)2 Sn(S2CNEt2)2(1) and (PhCH2)2 Sn(S2CNC4H8)2(2) were synthesized by the reaction of dibenzyltin dichloride with dithiocarbamates and characterized by elemental analysis ,IR,^1H NMR and MS spectra.The crystal structures were determined by X-ray single crystal diffraction analysis.In both complexes,the tin atom is six-coordinated in a distorted octahedral configuration.In the crystals of 1,the molecular packing in unit cell reveals that the two adjacent molecules are symmetrically linked to each other in dimers by two Sn S interactions of 0.3816nm.In the crystals of 2,the molecules are packed in the unit cell in one-dimensional chain structure linked by weaker intermolecular S S conmtacts.     

New Stable Complexes of Au(III) with Biuret: X-ray Structure of cis-[Au(Biu)Br2]PPh4 and Ab Initio Investigation of cis-[Au(Biu)X2]−

Two anionic complexes of Au(III) with the bioligand biuret, cis-[Au(Biu)X₂]^? (BiuH₂=biuret, X=Cl, Br), have been synthesized and characterized. The molecular structure of cis-[Au(Biu)Br₂]PPh₄ has been determined by X-ray diffraction analysis. The complex anion has square-planar geometry with one deprotonated biuret dianion coordinated bidentately to the metal center via the terminal amino nitrogen atoms and two bromide ions in cis positions. There are no significant intermolecular Au-Au interactions in the solid state. Ab initio calculations of the geometric structure at different computational levels for biuret and both anionic complexes as well an IR study of the structures obtained are performed.     

Standard enthalpies of formation of Ce–Au congruent compounds (CeAu,CeAu2, and Ce14Au51)

The enthalpies of formation of Ce–Au congruent compounds (CeAu, CeAu₂, and Ce₁₄Au₅₁) have been determined at 1123 K and the standard enthalpies of formation at 298 K have been deduced from the measurements of enthalpy increments of single-phase samples. The following values (kJ/mole of atoms) are reported: Δ_fH°_1123 K (CeAu) = −75.2 ± 1.4, Δ_fH°_298 K (CeAu) = −76.2 ± 1.9, Δ_fH°_1123 K (CeAu₂) = −71.3 ± 2.0, Δ_fH°_298 K (CeAu₂) = −70.3 ± 2.2, Δ_fH°_1123 K (Ce₁₄Au₅₁) = −55.0 ± 1.7, and Δ_fH°_298 K (Ce₁₄Au₅₁) = −53.2 ± 1.9.     

Fabrication of hollow SiO2 and Au (core)–SiO2 (shell) nanostructures of different shapes by CdS template dissolution

Core–shell silica (SiO₂) coated CdS nanorods (NR) and nanospheres (NS) were prepared (SiO₂@CdS) by deposition of a Si–O–Si amorphous layer over the CdS surface through the hydrolysis of 3-mercaptopropyltrimethoxysilane and tetraethylorthosilicate. Nanoporous SiO₂ matrix (NPSM), hollow SiO₂ nanotubes (HSNT) and nanospheres (HSNS) useful for efficient adsorption and catalytic processes were prepared by chemical dissolution of CdS–NS (size: 9–10 nm) and CdS–NR (length: 116–128 nm and width: 6–11 nm) template from SiO₂@CdS with 2 M HNO₃. These SiO₂ nanostructures were characterized by optical absorption, TEM, EDX, SAED and BET surface area analysis. TEM images revealed the fabrication of slightly distorted HSNS (size: 9–12 nm) and closed HSNT (length: 30–45 nm and diameter: 9–14 nm) of shorter dimensions than the CdS–NR template used. The BET surface area (112–134 m² g^?1) of NPSM and HSNS is found to be larger than the surface area (29–51 m² g^?1) of SiO₂@CdS composites indicating hollow SiO₂ morphology. Silica coated Au (SiO₂@Au) composites formed by CdS dissolution from Au (2 wt%) deposited CdS–NR core-encapsulated into SiO₂ shell (SiO₂@Au–CdS–NR) exhibited a surface plasmon band at 550 nm and displayed high catalytic activity for 4-nitrophenol reduction by Au nanoparticle.     

Synthesis and structural characterization of camphanates of (−)-(2S3S,3S) and (+)-(2S,3R)-4-Phenyl-3-bromo-2-butanol diastereoisomers

The X-ray crystal structures of (–)-syn-4-phenyl-3-bromo-2-butyl camphanate (I) and (+-anti-4-phenyl-3-bromo-2-butyl camphanate (II) have been determined. Thesyn diastereoisomer of bromohydrin has the (2S,3S) absolute configuration whereas theanti diastereoisomer has the (2S,3R) absolute configuration. The crystallized derivatives I and II have been obtained by the reaction of each stereoisomer of bromohydrin, synthesized by reduction with baker's yeast, with (1S)-camphanic chloride. Crystal data: (I) C₂₀H₂₅BrO₄:M _w: 409.32; orthorhombic,P2₁2₁2₁;a=11.245(3),b=12.086(1),c=14.512(4) å; Z=4; finalR=0.053 for 1819 observed reflections. (II) C₂₀H₂₅BrO₄;M _w=409.32; monoclinic, P2₁;a=11.352(1),b=6.378(1),c=14.255(2) å,=110.38(1);Z=2; finalR=0.045 for 1672 observed reflections.     

Chemisorption of the [AuCl4]− anion by cadmium cyclo-pentamethylenedithiocarbamate and the resulting bound-gold(III) species: The supramolecular structure and thermal behavior of the polynuclear complexes ([Au{S2CN(CH2)5}2]2[CdCl4]) n and ([Au{S2CN(CH2)5}Cl2]) n

The interaction between cadmium cyclo-pentamethylenedithiocarbamate (chemisorbent Ia) and the [AuCl₄]^? anion in 2 M HCl has been investigated. The state of the chemisorbent in contact with AuCl₃ solutions has been probed by ¹¹³Cd MAS NMR spectroscopy. The heterogeneous reactions in the system, including gold(III) chemisorption from the solution and partial ion exchange, yield the gold(III)-cadmium heteropolynuclear complex ([Au{S₂CN(CH₂)₅}₂]₂[CdCl₄]) _n (I) and the polynuclear mixed-ligand complex ([Au{S₂CN(CH₂)₅}Cl₂]) _n (II). The crystal and molecular structures of these compounds have been determined by X-ray crystallography. The main structural units of the compounds are the complex cation [Au{S₂CN(CH₂)₅}₂]⁺, [CdCl₄]^2? anion (in I), and Au{S₂CN(CH₂)₅}Cl₂ molecule (in II). The further structural self-organization of the complexes at the supramolecular level is due to secondary Au...S and Au...Au bonds. [Au₂{S₂CN(CH₂)₅}₄]²⁺ dinuclear cations form in the structure of I, which then polymerize into ([Au₂{S₂CN(CH₂)₅}₄]²⁺) _n chains. In the structure of II, adjacent Au{S₂CN(CH₂)₅}Cl₂ molecules join by forming pairs of asymmetric secondary Au...S bonds, producing polymer chains with alternating antiparallel monomer units. The chemisorption capacity values calculated for cadmium cyclo-pentamethylenedithiocarbamate from gold(III) binding reactions are 455 and 910 mg of gold per gram of sorbent. The gold recovery conditions have been determined by investigating the thermal behavior of I and II by synchronous thermal analysis. The multistep thermal destruction of ionic complex I includes the thermolysis of its carbamate moiety and [CdCl₄]_2? (which liberates gold metal and cadmium chloride and yield some amount of CdS) and CdCl₂ and CdS evaporation. The thermolysis of II proceeds via the formation of Au₂S and AuCl as intermediate compounds. In both cases, the ultimate pyrolysis product is elemental gold.     

The Unprecedented [S4N2O10]2− Anion in the Molecular Gold Complexes [Au2Br2(S4N2O10)2] and [Au2Cl2(S4N2O10)2](S2O5Cl2)

The reaction of hexachlorophosphazene, P₃N₃Cl₆, with SO₃ and the gold halides AuCl₃ and AuBr₃, respectively, leads to the new cyclic anionic tetramer, [S₄N₂O₁₀]²⁻, which is coordinated to Au³⁺ in the dimeric complexes [Au₂X₂(S₄N₂O₁₀)₂] (X=Cl, Br). The [S₄N₂O₁₀]²⁻ anion can be seen as the condensation product of two sulfate anions, [SO₄]²⁻_, and two amidosulfate anions, [NH₂SO₃]⁻.     

A Convenient Synthesis of (S)-2-Methyl and (2S)-2,3-Dimethyl Butyl Phenylsulfones from (S)-(-)-3-Methyl-γ-butyrolactone

Suitably functionalized alkylphenylsulfones have been used as building blocks for the synthesis of several modified side-chains steroids¹. We describe here the synthesis of (S)-2-methyl and (2S)-2,3-dimethyl butyl phenylsulfones (4a) and (6), which can be used for the construction of the side chain of a few marine sterols² or brassinosteroids³ as well.     

Primary amino-functionalized N-heterocyclic carbene ligands as support for Au(I)···Au(I) interactions: structural, electrochemical, spectroscopic and computational studies of the dinuclear [Au2(NH2(CH2)2imMe)2][NO3]2

The N-heterocyclic carbene (NHC) precursor, 1-(2-aminoethyl)-3-methylimidazolium nitrate, [NH(2)(CH(2))(2)imMe)]NO(3) ([3][NO(3)]) reacted with Ag(2)CO(3) in dimethyl sulfoxide readily yielding a Ag(I)-(NHC-NH(2)) complex presenting limited stability in solution. The in situ carbene transfer reaction of the latter with [Au(tht)Cl] afforded the first example of a dinuclear gold(I) complex [Au(2)(NH(2)(CH(2))(2)imMe)(2)][NO(3)](2) ([5][NO(3)](2)) bearing a primary amino-functionalized NHC ligand. The complex has been characterized by NMR, mass spectrometry, X-ray crystallography and cyclic voltammetry; the electrochemical behaviour and photophysical properties of [5][NO(3)](2) have been also investigated and the experimental data have been compared with density functional theory (DFT) and Time Dependent (TDDFT) calculations. Single-crystal structural studies showed that the Au(I)-carbene compound contains dinuclear (AuL)(2) cations in which pairs of gold(I) centres are linked by a pair of bridging ligands, with a Au···Au aurophilic contact of 3.2332(17) ? that is maintained in solution as documented by the DFT calculations. Complex [5][NO(3)](2) is photoluminescent in solution at room temperature and the high energy emission peak at 410 nm is remarkably shifted with respect to the absorption band centered at 260 nm.     

Luminescent copper(I) halide adducts of [Au(im(CH2py)2)2]PF6 exhibiting short Au(I)···Cu(I) separations and unusual semibridging NHC ligands

The picolyl-substituted NHC complex [Au(im(CH(2)py)(2))(2)]PF(6) (1) reacts with two equivalents of copper(I) halides, affording compounds [Au(im(CH(2)py)(2))(2)(CuX)(2)]PF(6) (X = Cl, 2; Br, 3; I, 4). Each complex contains a nearly linearly coordinated [Au(NHC)(2)](+) center where the two picolyl groups on each im(CH(2)py)(2) ligand chelate a single copper atom. The Cu(I) center resides in a distorted tetrahedral environment and is coordinated to two pyridyl groups, a halide ion, and a gold metalloligand. The Au(I)-Cu(I) separations measure 2.7030(5), 2.6688(9), and 2.6786(10) ? for 2-4, respectively. Additionally, each Cu(I) center is further coordinated by a semibridging NHC ligand with short Cu-C separations of ~2.3 ?. In solution, these complexes dissociate the Cu(I) ion. In the solid state, 2-4 are photoluminescent with respective emission maxima of 512, 502, and 507 nm. The reaction of [Au(im(CH(2)py)(2))(2)]PF(6) with four equivalents of CuBr afforded the coordination polymer {[AuCu(2)Br(2)(im(CH(2)py)(2))(2)]Br·3CH(3)CN}(n) (5). This polymeric complex contains [Au(NHC)(2)](+) units interconnected by Cu(2)Br(2) dimers. In 5, the Au-Cu separations are long at 4.23 and 4.79 ?, while the Cu-Cu distance is considerably shorter at 2.9248(14) ?. In the solid state, 5 is photoluminescent with a broad band appearing at 533 nm.     

Solvothermal Syntheses of (H2en)2Sn2S6· en and[(H2hmda)3(Hhmda)2](Sn2S6)2Using SnCl4 and S8 as Starting Materials

Three thiostannates (H2en)2Sn2S6·en 1, (Hen)4Sn2S6 2 (en = ethylenediamine, a known compound)and [(H2hmda)3(Hhmda)2](Sn2S6)2 3 (hmda = hexamethylenediamine) were solvothermal conditions. Compound 1 crystallizes in the triclinic system, space group P(1) with a =8.7491(17), b = 10.704(2), c = 12.2031(19) (A), α = 74.888(13), β= 72.998(12), γ= 89.032(15)°, V= 1052.9(3) (A)3, Mr = 614.08, Z = 2, Dc = 1.937 g/cm3,μ = 2.966 mm-1, F(000) = 604, S = 1.211, R = 0.0579 and wR = 0.0770 for 3999 observed reflections with I ＞ 2σ(I); while 3 crystallizes in the triclinic system, space group P(1) with a = 9.8075(13), b = 10.8266(16), c = 14.303(2) A, α =88.611(10), β = 81.030(9), γ= 74.609(9)°, V = 1446.1(4) (A)3, Mr = 1448.78, Z = 1, Dc = 1.664g/cm3, μ = 2.173 mm-1, F(000) = 730, S = 1.173, R = 0.0457 and wR = 0.0667 for 5738 observed reflections with I ＞ 2σ(I). The compounds are composed of dimeric [Sn2S6]4- anions and protonated alkylenediamine cations.     

Synthesis and Structure Determination of (2S, 2′S)-3-Phenyl-2-(pyrrolidin-2′-yl)- propionic Acid

Abstract

Aβ²,β³-homoproline derivative, (2S, 2′S)-3-phenyl-2-(pyrrolidin-2′-yl)propionic acid, was synthesized starting from l-proline. After preparation of the (4S, 4aS)-4-benzyl-4a,5,6,7-tetrahydro-pyrrolo-[1,2-c]pyrimidine-1,3-dione under a mild condition, the absolute configuration of target compound was assigned using 2D H-H COSY and H-H NOESY technologies.     

An efficient and stereoselective synthesis of (2S,1′S,2′S)-2-(carboxycyclopropyl) glycine (LCCG-I): conformationally constrained l-glutamate analogues

Conformationally restricted metabotropic glutamate receptor agonist (2S,1′S,2′S)-2-(Carboxycyclopropyl) glycine (LCCG-I) 1 have been efficiently synthesized in a stereoselective manner. A convenient five step synthesis of 1 from readily available (−)-dimenthyl (1S,2S)-cyclopropane-1,2-dicarboxylate 5 in 49% overall yield is described.     

Interconversion of (R) and (S)-α-hydroxy esters: precursors of (S) and (R)-o-benzyl-α-hydroxylamino acid esters of high optical purity

(R)- and (S)-α-hydroxy esters 5 are interconverted via their triflates 6 in high chemical as well as optical yields by reaction with dimethylformamide. The same triflates are efficiently converted into N-hydroxy-α-amino acid derivatives 7 of high optical purity.     

Synthesis of (3S,5R)-cis- and (3S,5S)-trans-3,5-Dimethylvalerolactones and Their Conversion to Biotransformation Products of (S)-5-Ethyl-5-(2′-pentyl)barbituric Acid

(R,S)-5-Ethyl-5-(2′-pentyl)barbituric acid (I)^1,2 is metabolized in vivo to give all four possible optical isomers of 5-ethyl-5-(3′-hydroxy-1′-methylbutyl)barbituric acid (II). ^3,4 From metabolism studies of pure (1′S)- I and (1′3)-I, Palmer and co-workers^4,5 were able to determine the relative amounts of each of the four isomers formed. These studies showed that (1′S)-I gave mainly one enantiomer of (1′S)-II, whereas (1′R)-I gave approximately equal amounts of both (1′R)-II enantiomers.     

Cross sections and isomeric ratios in197Au(α, 2pn)198(m,g)Au reactions

Excitation functions for the production of^198mAu,¹⁹⁸Au,^198(m+g)Au, by (, 2pn) reactions on gold and isomeric ratios for¹⁹⁸Au were determined experimentally. The method of activation of metallic foils was employed. The irradiations were performed in the isochronous cyclotron at Karlsruhe (Germany) with -particles at 90 MeV. Gamma-spectrometry by means of an intrinsic Ge detector was used to determine the nuclides produced. In addition, a comparison between the cross sections obtained and a calculation using the hybrid model of pre-equilibrium reactions, in combination with the statistical model development by ERNST is presented.     

Co(III) and Cr(III) complexes of diphosphadithia ligands and the crystal structure of [CoCl2(L3)]PF6·CH2Cl2 (L3=Ph2P(CH2)2S(o-C6H4)S(CH2)2PPh2)

[CrX₃(thf)₃] (X=Cl or Br) reacts with L (L=L¹–L³ or Ph₂[14]aneP₂S₂) (L¹=Ph₂P(CH₂)₂S(CH₂)₂S(CH₂)₂PPh₂, L²=Ph₂P(CH₂)₂S(CH₂)₃S(CH₂)₂PPh₂, L³=Ph₂P(CH₂)₂S(o-C₆H₄)S(CH₂)₂PPh₂, Ph₂[14]aneP₂S₂=4,8-diphenyl-1,11-dithia-4,8-diphosphacyclotetradecane) and TlPF₆ in MeNO₂ solution to yield the distorted octahedral complexes [CrX₂(L)]PF₆ as green coloured solids in high yield. UV/visible spectroscopy suggests that these are cis-dihalo species and they have also been characterised by IR spectroscopy, electrospray mass spectrometry and microanalyses. The Co(III) analogues [CoX₂(L)]⁺ are readily prepared in a two-stage reaction, involving treatment of CoX₂·6H₂O with L (L=L¹–L³) and NH₄PF₆ in EtOH solution to give a green/brown solid, followed by halogen oxidation of this product in CH₂Cl₂ solution using X₂/CCl₄, to give the final products as brown coloured solids. A mixture of PF₆⁻ and [CoX₄]²⁻ anions are present in the final Co(III) compounds in varying ratios. Crystal structures of [CoCl₂(L²)]₂[CoCl₄]·4H₂O and [CoCl₂(L³)]PF₆·CH₂Cl₂ confirm tetradentate P₂S₂ coordination of L in each case, with mutually cis halogens completing the distorted octahedral geometry. In both cases the complex cation adopts the cis-α form in the solid state and this is also consistent with the solution ³¹P{¹H} NMR spectroscopic data. ⁵⁹Co NMR spectroscopy reveals a very broad single resonance at ≈3200 ppm for these species.     

Facile Synthesis of (S,S)‐1,2‐Diacylamides and (S,S)‐1,2‐Diamines with C 2‐Symmetry

A series of chiral vicinal tertiary diacylamides with C ₂‐symmetry was synthesized from (S)‐α‐phenylethylamine, different aromatic aldehydes, and oxalyl chloride. The diacylamides obtained were then reduced to afford chiral vicinal diamines with C ₂‐symmetry. We propose that the diacylamides existed in four stable conformational isomers in solution because of the dihedral angle between acylamide bonds.     

Synthesis of (S)-(−)-β-cuparenone and (S)-(−)-cuparene

A short and efficient synthesis of the title compounds is described. (S)-(−)-β-Cuparenone was prepared in 31% yield from p-tolualdehyde and mesityl oxide in eight steps. Absolute stereochemistry was established by means of a diastereoselective cyclopropanation using (R,R)-hydrobenzoin as a recoverable auxiliary.