N-ferrocenoyl benzotriazole: A convenient tool for the synthesis of ferrocenoyl esters

A new synthesis methodology has been presented for the preparation of the ferrocenoyl esters. Ferrocene carboxylic acid was derivatized using direct 1H-benzotriazole/SOCl₂ methodology to prepare N-ferrocenoyl benzotriazole as a convenient tool for the functionalization of ferrocene ring. N-ferrocenoyl benzotriazole was reacted with alcohols in mild conditions to prepare ferrocenoyl esters in high purity and in good yield. The solid state structure of benzyl-1-ferrocenoate, 2f, has also been determined by X-ray crystallography. In the crystal structure, intermolecular C-H···O hydrogen bonds link the molecules into a two-dimensional network. The π···π contacts between the cyclopentadiene rings and cyclopentadiene and phenyl rings, [centroid-centroid distances = 3.296(1) and 3.750(1) Å] may further stabilize the structure. Two weak C-H···π interactions are also found.     

Cleavage of alkoxycarbonyl protecting groups from carbamates by t-BuNH2

An efficient, simple protocol for the selective cleavage of a variety of N-alkoxycarbonyl protecting groups by t-BuNH₂/MeOH is described. The scope of the procedure was explored for a series of indole, aniline and pyrrolidine carbamate derivatives containing other potentially reactive functional groups affording a clean cleavage of the carbamate group.     

Stille carbonylation of N-protected bromomethylindoles

A variety of N-protected indolylmethylbromides are carbonylated using 5 mol % Pd(PPh₃)₂Cl₂ under Stille conditions in the presence of an alcohol to afford the corresponding methyl/ethyl esters.     

Syntheses and structures of zinc and tin(II) compounds with hemilabile N-silyl-tert-butylamido and N-silyl-p-tolylamido ligands that contain pendent tert-butoxy groups

Syntheses and solid-state structures of zinc and tin(II) compounds, containing the N-silyl-amide ligands (O^tBu)(NR)SiMe₂, R = ^tBu (L^tBu), or R = p-tolyl (L^pTol), are reported. The N-silyl amines were synthesized by modified published procedures from commercially available Me₂SiCl₂, ^tBuOH, and ^tBuNH₂, or p-Me-C₆H₄NH₂, respectively. Treatment of SnCl₂ with LiL^pTol furnished Sn(L^pTol)₂, which was X-ray structurally characterized and shown to contain two covalent Sn-N bonds and two asymmetrical O → Sn donor bonds. The single-crystal X-ray structure of Sn(L^tBu)₂ revealed a much more symmetrically-coordinated, pseudo-trigonal-bipyramidal tin atom. Aminolysis of diethylzinc with HL^pTol produced [EtZn(L^pTol)]₂, which crystallized as a centrosymmetric dimer, containing four-coordinate zinc atoms connected by bridging amides. Zinc dichloride, by contrast, reacted with two equivalents of LiL^tBu to produce the homoleptic, pseudo-spirocyclic Zn(L^tBu)₂.     

Microwave-assisted deformylation of N-aryl formamide by KF on basic Al2O3

The formyl group was successfully removed from N-aryl formamide by KF on a solid support of basic Al₂O₃ in 4-20 min with microwave irradiation. The conditions mimic base-catalyzed hydrolysis of formamide and are compatible with carbamates and t-butyl esters, but not methyl, ethyl, and benzyl esters.     

Calorimetric investigation of the effect of hydroxyanthraquinones in Rheum officinale Baill on Staphylococcus aureus growth

The inhibitory effects of five hydroxyanthraquinones (HAQs) from root and rhizoma of Rheum officinale Baill, a traditional Chinese medicinal (TCM) herb, on Staphylococcus aureus growth were investigated by calorimetry. The power-time curves of S.aureus with and without HAQ were acquired and the extent and duration of inhibitory effects on the metabolism evaluated by growth rate constants (k₁, k₂), half inhibitory ratio (IC₅₀), maximum heat output (P_max) and peak time (t_p). The value of k₁ and k₂ of S. aureus in the presence of the five HAQs decreased with the increasing concentrations of HAQs. Moreover, P_max was reduced and the value of t_p increased with increasing concentrations of the five drugs. The inhibitory activity varied for different drugs. IC₅₀ of the five HAQs was 4 μg ml⁻¹ for emodin, 3.5 μg ml⁻¹ for rhein, 10 μg ml⁻¹ for aloe-emodin, 1000 μg ml⁻¹ for chrysophanol, 1600 μg ml⁻¹ for physcion. The sequence of antimicrobial activity of the five HAQs: rhein > emodin > aloe-emodin > chrysophanol > physicion.     

Catalytic, PMe3-mediated conversion of secondary nitroalkanes to ketones: a very mild Nef-type process

Aliphatic secondary nitro compounds are converted to ketones at room temperature, usually in 90-100% yields, by a one-pot reaction with 220-250 mol % of trimethylphosphine (PMe₃) and 50-100 mol % of ^tBuC₆H₄SSC₆H₄^tBu or PhthN-SePh, or 20 mol % of both additives. Thus, very mild catalytic variants of the reductive Nef-like reactions are disclosed.     

Development of a high-performance liquid chromatography-fluorescence detection method for analyzing nonylphenol/dinonylphenol-polyethoxylate-based phosphate esters

A novel reversed phase HPLC method for the simultaneous analysis of surfactants containing nonylphenol/dinonylphenol-polyethoxylates and their o-phosphate esters is reported, in which eluting substances are detected fluorescently. Their chemical structures were elucidated by direct infusion electrospray-mass spectrometry in positive mode. The limits of quantification and range of the method were determined to be 0.1 mg and 0.1–100 mg surfactant L⁻¹, respectively, with a reproducibility (RSD) at a concentration of 38 mg surfactant L⁻¹ of 5.6%. The accuracy was determined by spiking selected process water samples with known amounts of surfactant, and recoveries were typically in the 82–102% range.     

Synthesis, structure, and bridge-terminal alkyl exchange kinetics of pyrazolate-bridged dialuminum complexes containing bridging n-alkyl groups

Treatment of triethylaluminum with 3,5-diphenylpyrazole in a 2:1 stoichiometry afforded the ethyl-bridged complex Et₂Al(μ-Ph₂pz)(μ-Et)AlEt₂ (79%) as a colorless crystalline solid. Treatment of tri-n-propylaluminum with 3,5-di-tert-butylpyrazole in a 2:1 stoichiometry afforded the n-propyl-bridged complex (nPr)₂Al(μ-tBu₂pz)(μ-nPr)Al(nPr)₂ (63%) and the dimeric complex [(nPr)₂Al(μ-tBu₂pz)]₂ (3%), respectively, as colorless crystalline solids. Treatment of tri-n-propylaluminum (1 equiv.) or triisobutylaluminum (1 or 2 equiv.) with 3,5-di-tert-butylpyrazole afforded exclusively the dimeric complexes [(nPr)₂Al(μ-tBu₂pz)]₂ (68%) or [(iBu)₂Al(μ-tBu₂pz)]₂ (96%), respectively, as colorless crystalline solids. The solid state structures of Et₂Al(μ-Ph₂pz)(μ-Et)AlEt₂ and (nPr)₂Al(μ-tBu₂pz)(μ-nPr)Al(nPr)₂ consist of 3,5-disubstituted pyrazolato ligands with a di-n-alkylalumino group bonded to each nitrogen atom. An ethyl or n-propyl group acts as a bridge between the two aluminum atoms. The kinetics of the bridge-terminal exchange was determined for the bridging n-alkyl complexes by ¹³C NMR spectroscopy, and afforded ΔH^‡ = 1.5 ± 0.1 kcal/mol, ΔS^‡ = −46.8 ± 39.0 cal/K mol, and for Et₂Al(μ-Ph₂pz)(μ-Et)AlEt₂ and ΔH^‡ = 1.7 ± 0.1 kcal/mol, ΔS^‡ = −46.6 ± 43.4 cal/K mol, and for (nPr)₂Al(μ-tBu₂pz)(μ-nPr)Al(nPr)₂. The negative values of ΔS^‡ imply ordered transition states relative to the ground states, and rotation along the N-AlR₃ vector without aluminum-nitrogen bond cleavage is proposed.     

Modification and chemical transformation of Si(1 1 1) surface

Modification of hydrogen-terminated Si(1 1 1) surfaces by hydrosilylation of activated alkenes and further chemical transformation of the modified surfaces is reported. A Si(1 1 1)-H surface was reacted with activated alkenes such as acrylate esters, acrylonitrile, and maleic anhydride under mild conditions to give modified surfaces with terminal functional groups. A modified surface with a terminal ester group was reduced by LiAlH₄ to give a hydroxy-terminated surface, and the hydroxy-terminated surface was transformed to a bromo-terminated surface. XPS analysis revealed that the brominated surface (Si(1 1 1)-CH₂CH₂CH₂Br) had 32% coverage with the 3-bromopropyl group. Ester and amide formation reactions were carried out on hydroxy- and carboxy-terminated Si surfaces by reaction with tert-butoxycarbonyl glycine, glycine tert-butyl ester, 2,2,2-trifluoroethanol and 4-trifluoromethylbenzyl alcohol in the presence of carbodiimide. XPS characterization indicated that the esters and amide were successfully formed with coverage ranging from 16% to 58%. Coverage ratios of octadecyl ester modified surfaces were also estimated by combination of surface reduction and gas chromatography analysis to be 25-35%.     

A simple procedure for the esterification of alcohols with sodium carboxylate salts using 1-tosylimidazole (TsIm)

An efficient and selective method for esterification of alcohols using N-(p-toluenesulfonyl)imidazole (TsIm) is described. In this method, alcohols are refluxed with a mixture of RCO₂Na (R: alkyl and aryl), TsIm, and triethylamine in the presence of catalytic amounts of tetra-n-butylammonium iodide (TBAI) in DMF to afford the corresponding esters in good yields. This methodology is highly efficient for various structurally diverse alcohols with selectivity for ROH: 1° > 2° > 3°.     

Efficient, solventless N-Boc protection of amines carried out at room temperature using sulfamic acid as recyclable catalyst

A simple, rapid, and efficient protocol for the chemoselective N-Boc protection of amines using sulfamic acid as catalyst is described. N-Boc protection of various structurally diverse aliphatic, aromatic, alicyclic, and heterocyclic amines (1°, 2°, 3°) was carried out with (Boc)₂O using sulfamic acid as catalyst (5 mol %) at room temperature under solventless conditions. The advantages of this method are simplicity, shorter reaction times (1-15 min), a cost-effective catalyst, and excellent isolated yields (90-100%); it is also environmentally benign. Moreover, the combined use of ultrasound and sulfamic acid achieves a synergic effect that is especially marked in the N-Boc protection of deactivated (sterically hindered and electron-deficient) amines. The catalyst possesses distinct advantages: ease of handling, cleaner reactions, high activity, and excellent chemoselectivity.     

Nano TiO2/SO4 as a heterogeneous solid acid catalyst for the synthesis of 5-substited-1H-tetrazoles

An efficient and economical protocol for the synthesis of 5-substituted-1H-tetrazoles from various nitriles and sodium azide is reported using nano TiO₂/SO₄²⁻ as an effective heterogeneous catalyst. A wide variety of aryl nitriles underwent [3 + 2] cycloaddition to afford tetrazoles in good to excellent yields.     

Swelling and network parameters of crosslinked thermoreversible hydrogels of poly(N-ethylacrylamide)

Samples of Poly(N-ethylacrylamide) (PEA) have been synthesized by free radical polymerization in water using N,N′-methylene bis-acrylamide (BIS) as crosslinker. Hydrogels obtained by swelling them in water, 15 wt% KCl and 1 wt% sodium dodecyl sulphate (SDS) were examined by gravimetric, dimensional and compression-strain measurements to afford values of swelling ratio, polymer-solvent interaction parameters, elastic moduli and effective crosslinking density ν_e. Crosslinking inefficiency is evidenced by the low value (0.23) of ν_e relative to the theoretical crosslinking density ν_t based on the content of BIS in the synthesis. A small but finite extrapolated value of ν_e at ν_t = 0 is indicative of hydrophobic physical interactions. In water at 298 K increasing the content of BIS leads to a decrease in swelling and increases in values of elastic moduli and polymer-water interaction parameter. At a fixed content of BIS the values of ν_e and the elastic moduli exhibit an unusual increase with temperature, the crosslinking thus being thermally reversible. It is proposed that this results from a balance between hydrophobic interaction and breakage of hydrophilic hydrogen bonding. Although KCl in the medium decreases the swelling compared with that in water, the opposite effect occurs on incorporation of SDS, which is assumed to confer some polyelectrolyte character to the PEA chains. The finding, that these two swelling media reduce the values of ν_e and elastic moduli cf the value in water, has not been resolved satisfactorily.     

Barium alginate caged Fe3O4@C18 magnetic nanoparticles for the pre-concentration of polycyclic aromatic hydrocarbons and phthalate esters from environmental water samples

The hydrophobic octadecyl (C₁₈) functionalized Fe₃O₄ magnetic nanoparticles (Fe₃O₄@C₁₈) were caged into hydrophilic barium alginate (Ba²⁺-ALG) polymers to obtain a novel type of solid-phase extraction (SPE) sorbents, and the sorbents were applied to the pre-concentration of polycyclic aromatic hydrocarbons (PAHs) and phthalate esters (PAEs) pollutants from environmental water samples. The hydrophilicity of the Ba²⁺-ALG cage enhances the dispersibility of sorbents in water samples, and the superparamagnetism of the Fe₃O₄ core facilitates magnetic separation. With the magnetic SPE technique based on the Fe₃O₄@C₁₈@Ba²⁺-ALG sorbents, it requires only 30 min to extract trace levels of analytes from 500 mL water samples. After the eluate is condensed to 0.5 mL, concentration factors for both phenanthrene and di-n-propyl-phthalate are over 500, while for other analytes are about 1000. The recoveries of target compounds are independent of salinity and solution pH under testing conditions. Under optimized conditions, the detection limits for phenanthrene, pyrene, benzo[a]anthracene, and benzo[a]pyrene are 5, 5, 3, and 2 ng L⁻¹, and for di-n-propyl-phthalate, di-n-butyl-phthalate, di-cyclohexyl-phthalate, and di-n-octyl-phthalate are 36, 59, 19, and 36 ng L⁻¹, respectively. The spiked recoveries of several real water samples for PAHs and PAEs are in the range of 72-108% with relative standard deviations varying from 1% to 9%, showing good accuracy of the method. The advantages of the new SPE method include high extraction efficiency, short analysis time and convenient extraction procedure. To the best of our knowledge, it is unprecedented that hydrophilic Ba²⁺-ALG polymer caged Fe₃O₄@C₁₈ magnetic nanomaterial is used to extract organic pollutants from large volumes of water samples.     

Geometry and chemical bonding in polyhedral boranes, metallaboranes, and dimetallaboranes: From closo to isocloso to oblatocloso polyhedra

The geometry and chemical bonding in the closo metal-free boranes and the isoelectronic carboranes and C₂B_n−2H_n with 2n + 2 skeletal electrons are based on the most spherical deltahedra with a preference for degree 5 vertices, particularly for the boron atoms. Such deltahedral boranes can be considered to be three-dimensional aromatic systems, as indicated by strongly diatropic nucleus independent chemical shift values for (n = 6, 8, 9, 12). Metallaborane structures, particularly those with 9-11 vertices and only 2n rather than 2n + 2 apparent skeletal electrons, are often based on isocloso deltahedra with the metal atom at a degree 6 vertex. Dimetallaborane structures, particularly the rhenium derivatives Cp₂Re₂B_n−2H_n−2 (8 ? n ? 12), are based on highly non-spherical and very oblate deltahedra with the metal atoms typically at degree 6 or 7 vertices, which are the lowest curvature sites of the deltahedra. A viable model for the skeletal bonding in such dimetallaboranes can be developed if each of the two metal vertices is assumed to contribute five internal orbitals to the skeletal bonding. This leads to 2n + 4 skeletal electrons, which are partitioned into n surface bonds and a formal metal-metal double bond inside the oblate deltahedron.     

Theoretical study of intra- and inter-chain magnetic interactions in [Ni(chxn)2Br]Br2

The intra- and the inter-chain magnetic interactions in [Ni(chxn)₂Br]Br₂, which is one of the typical one-dimensional (1-D) MX complexes are examined by using an unrestricted hybrid DFT (UB3LYP) method. Calculated effective exchange integral (J) value along the 1-D chain is 2J_Intra = −4016 K and is close to an experimental result (−3600 K). On the other hand, a very weak anti-ferromagnetic inter-chain interaction through Br⁻ ions is observed. The value is estimated to be 2J_Inter = −2 to −6 K. In addition to the J values, transfer integral (t), on-site Coulomb repulsion (U) and charge transfer energy (E^CT) values along the 1-D chain are also estimated to be 0.46, 2.46 and 0.6 eV, respectively.     

Facile nucleophilic fluorination by synergistic effect between polymer-supported ionic liquid catalyst and tert-alcohol reaction media system

A highly efficient method was developed for nucleophilic fluorination using an alkali metal fluoride through the synergistic effect of the polymer-supported ionic liquid (PSIL) as a catalyst and tert-alcohol as an alternative reaction media. This PSIL/tert-alcohol system not only enhances the reactivity of alkali metal fluorides and reduces the formation of by-products but also allows the use of a polymer-supported catalyst protocol. As an example, the nucleophilic fluorinations of the model compound, 2-(3-bromopropoxy)naphthalene, with CsF using only tert-amyl alcohol as solvent (for 2 h reaction time), 0.5 equiv of PS[hmim][BF₄] in CH₃CN (for 12 h reaction time), and 0.5 equiv of PS[hmim][BF₄] in tert-amyl alcohol (which is a PSIL/tert-alcohol system for the synergistic effect; for 2 h reaction time) provided 18, 40, and 84% yield, respectively. The characteristics of the nucleophilic fluorination reactions of some halo- and alkanesulfonyloxyalkane systems to the corresponding fluoroalkanes using various alkali metal fluorides are also reported.     

The structures of (phenylato)(N-2-thiophenecarboxamido-meso-tetraphenylporphyrinato)mercury(II) and bisphenylmercury(II) complex of 21-(4-tert-butyl-benzenesulfonamido)-5,10,15,20-tetraphenylporphyrin

The reaction of PhHgOAc with N-NHCO-2-C₄H₃S-Htpp (5) and N-p-HNSO2C6H4^tBu-Htpp (4) gave a mercury (II) complex of (phenylato) (N-2-thiophenecarboxamido-meso-tetra phenylporphyrinato)mercury(II) 1.5 methylene chloride solvate [HgPh(N-NHCO-2-C₄H₃S-tpp) · CH₂Cl₂ · 0.5C₆H₁₄;  6 · CH₂Cl₂ · 0.5C₆H₁₄] and a bismercury complex of bisphenylmercury(II) complex of 21-(4-tert-butyl-benzenesulfonamido)-5,10,15,20-tetraphenylporphyrin, [(HgPh)2(N-p-NSO₂C₆H₄^tBu-tpp); 7], respectively. The crystal structures of 6 · CH₂Cl₂ · 0.5C₆H₁₄ and 7 were determined. The coordination sphere around Hg(1) in 6 · CH₂Cl₂ · 0.5C₆H₁₄ and Hg(2) in 7 is a sitting-atop derivative with a seesaw geometry, whereas for the Hg(1) in 7, it is a linear coordination geometry. Both Hg(1) in 6 · CH₂Cl₂ · 0.5C₆H₁₄ and Hg(2) in 7 acquire 4-coordination with four strong bonds [Hg(1)–N(1) = 2.586(3) Å, Hg(1)–N(2) = 2.118(3) Å, Hg(1)–N(3) = 2.625(3) Å, and Hg(1)–C(50) = 2.049(4) Å for 6 · CH₂Cl₂ · 0.5C₆H₁₄; Hg(2)–N(1) = 2.566(6) Å, Hg(2)–N(2) = 2.155(6) Å, Hg(2)–N() = 2.583(6) Å, and Hg(2)–C(61) = 2.064(7) Å for 7]. The plane of the three pyrrole nitrogen atoms [i.e., N(1)–N(3)] strongly bonded to Hg(1) in 6 · CH₂Cl₂ · 0.5C₆H₁₄ and to Hg(2) in 7 is adopted as a reference plane 3N. For the Hg²⁺ complex in 6 · CH₂Cl₂ · 0.5C₆H₁₄, the pyrrole nitrogen bonded to the 2-thiophenecarboxamido ligand lies in a plane with a dihedral angle of 33.4° with respect to the 3N plane, but for the bismercury(II) complex in 7, the corresponding dihedral angle for the pyrrole nitrogen bonded to the NSO₂C₆H₄^tBu group is found to be 42.9°. In the former complex, Hg(1)²⁺ and N(5) are located on different sides at 1.47 and −1.29 Å from its 3N plane, and in the latter one, Hg(2)²⁺ and N(5) are also located on different sides at −1.49 and 1.36 Å form its 3N plane. The Hg(1)?Hg(2) distance in 7 is 3.622(6) Å. Hence, no metallophilic Hg(II)?Hg(II) interaction may be anticipated. NOE difference spectroscopy, HMQC and HMBC were employed to unambiguous assignment for the ¹H and ¹³C NMR resonances of 6 · CH₂Cl₂ ·  0.5C₆H₁₄ in CD₂Cl₂ and 7 in CDCl₃ at 20 °C. The ¹⁹⁹Hg chemical shift δ for a 0.05 M solution of 7 in CDCl₃ solution is observed at −1074 ppm for Hg(2) nucleus with a coordination number of four and at −1191 ppm for Hg(1) nucleus with a coordination number of two. The former resonance is consistent with that chemical shift for a 0.01 M solution of 6 in CD₂Cl₂ having observed at −1108 ppm for Hg(1) nucleus with a coordination number of four.     

Trapping enols of esters and lactones with diazomethane

A series of regioisomeric ketene-O,O-dialkyl acetals were prepared from ambident β-dicarbonylfuroindoles by trapping the enol tautomers of esters and lactones with diazomethane. Definitive structural characterization was accomplished by X-ray crystal structure determination on a ketene-O,O-dimethyl acetal (R = Me).