N,N′-bis(substituted-phenyl)oxamides and their dinuclear pentacoordinate nickel(II) complexes

The preparation, spectroscopic characterization and magnetic study of N,N′-bis(substituted-phenyl)oxamidate-bridged nickel(II) dinuclear complexes of formula {[Ni(N₃-mc)]₂(μ-CONC₆H₄-X)}(PF₆)₂ (N₃-mc = 2,4,4-trimethyl-1,5,9-triazacyclo-dodec-1-ene (Me₃-N₃-mc) or 2,4,4,9-tetramethyl-1,5,9-triazacyclododec-1-ene (Me₄-N₃-mc), X = 2-Cl, 4-Cl, 2-OCH₃, 4-OCH₃) are reported. These paramagnetic nickel(II) complexes have been characterized by both one- and two-dimensional (COSY) ¹H NMR techniques. The COSY spectrum of 5 has allowed to achieve the assignment of the phenyl protons of the N,N′-diphenyloxamidate. The crystal structures of [Ni(Me₃-N₃-mc)(μ-CONC₆H₄-4-Cl)]₂(PF₆)₂ (6), [Ni(Me₃-N₃-mc)(μ-CONC₆H₄-4-OMe)]₂(PF₆)₂ (8) and [Ni(Me₄-N₃-mc)(μ-CONC₆H₄-2-Cl)]₂(PF₆)₂ (9) have been determined and their magnetic properties have been studied. The value of magnetic coupling between the two nickel(II) ions across the oxamidate bridge [J = − 37.6 (6), −39.9 (8) and −39.7 cm⁻¹ (9)] is sensitive to the distortion of the coordination sphere of the metal ions and the topology of the molecular bridge.     

Ionic addition of t-butyl N,N-dibromocarbamate (BBC) to alkenes and cycloalkenes

The addition of t-butyl N,N-dibromocarbamate (BBC) to alkenes and cycloalkenes in the presence of BF₃·Et₂O proceeds smoothly at −20°C in CH₂Cl₂ affording upon reduction with aqueous Na₂SO₃ the corresponding β-bromo-N-Boc-amines. Immediate deprotection of these adducts with gaseous HCl yields β-bromoamine hydrochlorides in moderate yields. The regioselectivity typical for Markovnikov addition was observed for styrene. Stereospecific anti-addition of BBC to cyclohexene and (E)-hex-3-ene, as proven by ¹H NMR evidence, is compatible with an ionic addition pathway and can be rationalized by assuming the intermediate complex formation between BBC and BF₃.     

Vibrational intensities of liquid N-methylpiperidine

Thin film transmission spectra of liquid N-methylpiperidine were measured in the 4000–500 cm⁻¹ region, using cells of thicknesses ranging from 1 to 8.2 μm. The spectra of both components of the complex refractive index were determined from these data in the mid-IR. Vibrational intensities and other spectral data were calculated from the k(ν) spectrum. In this region 41 bands were detected and quantitatively described. The assignment of numerous bands was carried out. The results were compared with available literature data.     

The conformation of N-nitroso-N-methylaniline from microwave spectroscopy

The low resolution microwave spectrum of N-nitro,N-methylaniline shows only one series of μ_a R-branch bands. The value of B + C = 1584.6 MHz is consistent with this being the rotamer in which the benzene ring is exo to the nitroso group. The high resolution microwave spectra of the normal. CD₃ and two meta-D species show conclusively that this rotamer has a non-polar heavy atom skeleton. The rotational constants, the quantity Δ_c (= I_a + I_b − I_c) and the substitution coordinates are well reproduced by a molecular model based on the structures of aniline and N,N-dimethylnitrosamine in which the plane of the benzene ring is twisted by 30° relative to the heavy atom plane of the rest of the molecule.     

Photochemical reactions of electron-deficient olefins with N,N,N′,N′-tetramethylbenzidine via photoinduced electron-transfer

Photoinduced electron transfer reactions of several electron-deficient olefins with N,N,N′,N′-tetramethylbenzidine (TMB) in acetonitrile solution have been studied by using laser flash photolysis technique and steady-state fluorescence quenching method. Laser pulse excitation of TMB yields ³TMB* after rapid intersystem crossing from ¹TMB*. The triplet which located at 480 nm is found to undergo fast quenching with the electron acceptors fumaronitrile (FN), dimethyl fumarate (DMF), diethyl fumarate (DEF), cinnamonitrile (CN), -acetoxyacrylonitrile (AAN), crotononitrile (CrN) and 3-methoxyacrylonitrile (MAN). Substituents binding to olefin molecule own different electron-donating/withdrawing powers, which determine the electron-deficient property (π-cloud density) of olefin molecule as well as control the electron transfer rate constant directly. The detection of ion radical intermediates in the photolysis reactions confirms the proposed electron transfer mechanism, as expected from thermodynamics. The quenching rate constants of triplet TMB by these olefins have been determined at 510 nm to avoid the disturbance of formed TMB cation radical around 475 nm. All the values approach or reach to the diffusion-controlled limit. In addition, fluorescence quenching rate constants have been also obtained by calculating with Stern–Volmer equation. A correlation between experimental electron transfer rate constants and free energy changes has been explained by Marcus theory of adiabatic outer-sphere electron transfer. Disharmonic k_q values for CN and CrN in endergonic region may be the disturbance of exciplexs formation.     

Synthesis of N,N′-dimethyl-N,N′-dibutyl malonamide functionalized polymer and its sorption affinities towards U(VI) and Th(IV) ions

A novel chelating polymeric material was synthesized by chemical anchoring of N,N′-dimethyl-N,N′-dibutyl malonamide (DMDBMA) with chloromethylated polystyrene-divinyl benzene polymer. The polymeric material thus prepared was characterized by ¹³C NMR, FT-IR spectroscopy and CHN elemental analysis. The fabricated polymeric material exhibited superior binding for hexa-valent and tetra-valent metal ions such as U(VI) and Th(IV). Various physico-chemical properties of the functionalized polymer like phase adsorption kinetics, metal sorption mechanism and metal sorption capacity was studied in the static method. Adsorption kinetics studies show that <20 min was sufficient for >99.99% adsorption of Th(IV) and U(VI). The kinetics for adsorption of U(VI) and Th(IV) was found to follow the first order Lagergren rate kinetics. Adsorption of U(VI) on the malonamide functionalized polymer followed the Langmuir adsorption isotherm. The Langmuir monolayer adsorption phenomenon was also confirmed by the theoretical approach calculated based on the adsorption kinetics. The metal sorption capacities for uranium and thorium were found to be 18.78 ± 1.53 mg and 15.74 ± 1.59 mg/g of the chelating polymer at 3 M HNO₃, respectively.     

Poly(N,N-dimethylaminoethyl methacrylate)–poly(ethylene oxide) copolymer membranes for selective separation of CO2

A series of copolymers containing ether oxygen groups and amino groups were prepared based on N,N-dimethylaminoethyl methacrylate (DMEMA) and polyethylene glycol methyl ether methyl acrylate (PEGMEMA). The effect of PEGMEMA content in the copolymer on density, free volume, mechanical performance, and H₂, CO₂, N₂ and CH₄ gas transport properties of the copolymer was determined. Free volume was characterized using the polymer density and group contribution theory. The permeability of the copolymer to CO₂ is high, and both the CO₂/N₂ and CO₂/H₂ selectivities are high. For example, the permeability coefficient of PDMAEMA–PEGMEMA-90 (“90” represents the weight percent of PEGMEMA) to CO₂ is 112 Barrer and the CO₂/N₂ and CO₂/H₂ selectivity coefficients are 31 and 7, respectively. The effect of the temperature on gas transport properties was also determined. Finally, the potential application of the copolymer membranes for CO₂/light gases separation was explored.     

Surface activity and thermodynamic of micellization and adsorption for isooctylphenol ethoxylates, phosphate esters and their mixtures with N-diethoxylated perfluorooctanamide

Three nonionic surfactants; p-isooctylphenol ethoxylates p-[i-OPE10], p-[i-OPE15], and p-[i-OPE20], were phosphorylated to produce three anionic phosphate ester surfactants. In addition, N-diethoxylated perfluorooctanamide (N-DEFOA) was also prepared. The surface and thermodynamic properties of the three types of surfactants and mixtures of the fluorocarbon surfactant (FC) with the hydrocarbon surfactants (HC) have been investigated. Surface tension as a function of concentration of the surfactant in aqueous solution was measured at 30, 40, 50 and 60°C, using the spinning drop technique. From these measurements the critical micelle concentration (CMC), the surface tension at the CMC (γ_CMC), the maximum surface excess concentration (Γ_max), the minimum area per molecule at the aqueous solution/air interface (A_min), and the effectiveness of surface tension reduction (π_CMC), were calculated. The thermodynamic parameters of micellization (ΔG_mic, ΔH_mic, ΔS_mic) and of adsorption (ΔG_ad, ΔH_ad, ΔS_ad) for these surfactants and their mixtures were also calculated. Structural effects on micellization, adsorption and effectiveness of surface tension reduction are discussed in terms of these parameters. The results show that the FC surfactant and its mixtures with HC surfactants enhance the efficiency in surface tension reduction and adsorption in the mixed monolayer at the aqueous solution/air interface, and also, reduce γ_CMC and the tendency towards micellization.     

First steps in radiation-induced hydrogel synthesis: radical formation and oligomerization in dilute aqueous N-isopropylacrylamide solutions

The reactions of hydroxyl radical, hydrogen atom and hydrated electron intermediates of water radiolysis with N-isopropylacrylamide (NIPAAm) were studied by pulse radiolysis in dilute aqueous solutions. OH, H and e_aq⁻ react with NIPAAm with rate coefficient of (6.9±1.2)×10⁹, (6.6±1)×10⁹, and (1.0±0.2)×10¹⁰ mol⁻¹ dm³ s⁻¹. In OH and H radical addition to the double bond mainly -carboxyalkyl type radicals form, (OHCH₂CH^√C(N-i-C₃H₇)O and CH₃CH^√C(N-i-C₃H₇)O). In reaction of e_aq⁻ oxygen atom centered radical anion is produced (CH₂CHC^√(N-i-C₃H₇)O⁻), the anion undergoes reversible protonation with pK_a=8.7. There is also an irreversible protonation on the β-carbon atom that produces the same radical as forms in H atom reaction (CH₃CH^√C(N-i-C₃H₇)O). The -carboxyalkyl type radicals at low NIPAAm concentration (0.1–1 mmol dm⁻³) mainly disappear in self-termination reactions, 2k_t,m=8.4×10⁸ mol⁻¹ dm³ s⁻¹. At higher concentrations the decay curves reflect the competition of the self-termination and radical addition to monomer (propagation). The termination rate coefficient of oligomer radicals containing a few monomer units is 2k_t≈2×10⁸ mol⁻¹ dm³ s¹.     

The synthesis and x-ray structure of (N,N-dimethyldithiocarbamato)(n-butyl)diphenyltin(IV)

(N,N-Dimethyldithiocarbamato)(n-butyl)diphenyltin(IV), n-BuPh₂SnS₂NMe₂, crystallizes in the monoclinic space group P2₁/n with a 9.772(5), b 9.895(4), c 21.418(9) Å, β 95.81(3)⁰, V 2060 ų Z = 4, μ 14.4 cm⁻¹ The structure was determined by the heavy-atom technique from 3103 independent reflections measured at room temperature on an Enraf-Nonius four-circle CAD-4 diffractometer using monochromatized Mo-K radiation and refined to a final R value of 5.8%. The tin atom is essentially four-coordinated with a weak fifth tin-sulphur bond (Sn---S(2) 3.079(1) Å) considerably longer than the other (Sn---S(1) 2.466(1) Å). A comparison with the complex n-BuPhSn(C1)S₂CNEt₂ (Sn---S(1) 2.454(1) Å; Sn---S(2) 2.764(1) Å) suggests that enhanced steric factors are responsible for the preferential monodentate behaviour of the dithiocarbamate ligand in the title complex.     

Synthesis of 2-oxazolines mediated by N,N′-diisopropylcarbodiimide

N-(β-Hydroxy)amides can be cyclised by reaction with diisopropylcarbodiimide (DIC) to give the corresponding 2-oxazolines in high yields. The reaction requires only very mild Lewis-acid catalysis (5 mol % Cu(OTf)₂) and can be accomplished with simple heating, or in very short reaction times under microwave irradiation.     

Asymmetric Synthesis of Homoallylic Amines and Functionalized Pyrrolidines via Direct Amino-Crotylation of In Situ Generated Imines

The asymmetric synthesis of functionalized homoallylic amines and silyl functionalized pyrrolidines through the Lewis acid promoted condensation of chiral (E)-crotylsilanes with sulfonyl imines and in situ generated N-acyl imines is described. We had anticipated that this bond construction could be used in the asymmetric synthesis of the N-terminal amino acid subunit of the nikkomycins. Aryl sulfonyl imines condense with chiral silane reagents in the presence of BF₃·OEt₂ to form homoallylic arylsulfonyl amines with useful levels of syn selectivity. For cases involving aryl N-acyl imines we have learned that the temperature controls the course of the reaction. For instance, at temperatures of −78°C or below the major product is the pyrrolidine, while at higher temperatures (−30 to −20°C) the homoallylic amine is produced. For the cases studied, the [3+2]-annulation is limited to aryl imine derivatives, as alkyl- and branched- imines failed to produce the pyrrolidine derivatives: higher reaction temperatures promote the conversion of the annulation product to the homoallylic amines. In double stereodifferentiating reactions with in situ generated imines, good levels of selectivity were achieved in the formation of secondary amines bearing syn–anti and syn–syn stereochemical triads.     

MP2 study of substituent effects of 2-substituted alkyl ethyl methylcarbamates in homogeneous, unimolecular gas phase elimination reaction

Møller-Plesset MP2/6-31G method was used to examine the gas-phase elimination of 2-substituted alkyl ethyl N,N-dimethylcarbamates. The results of these calculations support a concerted non-synchronous six-membered cyclic transition state mechanism for carbamates containing a C_β–H bond at the alkyl side of the ester. These substrates produce the N,N-dimethylcarbamic acid and the corresponding olefin. The unstable intermediate, N,N-dimethylcarbamic acid, rapidly decomposes through a four-membered cyclic transition state to dimethylamine and CO₂ gas. Correlation of the logarithm of theoretical rate coefficients against original Taft's σ* values gave an approximate straight line (ρ*=−1.39, r=0.9558 at 360 °C). In addition to this fact, when log k_rel is plotted against the theoretical log k_rel for 2-substituted ethyl N,N-dimethylcarbamates a reasonable straight line (r=0.9919 at 360 °C) is obtained, suggesting similar mechanism.     

Structural and spectral studies of N-2-(pyridyl)-, N-2-(3-, 4-, 5-, and 6-picolyl)- and N-2-(4,6-lutidyl)-N′-2-thiomethoxyphenylthioureas

Structures of the following compounds have been obtained: N-(2-pyridyl)-N′-2-thiomethoxyphenylthiourea, PyTu2SMe, monoclinic, P2₁/c, a=11.905(3), b=4.7660(8), c=23,532(6) Å, β=95.993(8)°, V=1327.9(5) ų and Z=4; N-2-(3-picolyl)-N′-2-thiomethoxyphenyl-thiourea, 3PicTu2SeMe, monoclinic, C2/c, a=22.870(5), b=7.564(1), c=16.941(4) Å, β=98.300(6)°, V=2899.9(9) ų and Z=8; N-2-(4-picolyl)-N′-2-thiomethoxyphenylthiourea, 4PicTu2SMe, monoclinic P2₁/a, a=9.44(5), b=18.18(7), c=8.376(12) Å, β=91.62(5)°, V=1437(1) ų and Z=4; N-2-(5-picolyl)-N′-2-thiomethoxyphenylthiourea, 5PicTu2SMe, monoclinic, C2/c, a=21.807(2), b=7.5940(9), c=17.500(2) Å, β=93.267(6)°, V=2893.3(5) ų and Z=8; N-2-(6-picolyl)-N′-2-thiomethoxyphenylthiourea, 6PicTu2SMe, monoclinic, P2₁/c, a=8.499(4), b=7.819(2), c=22.291(8) Å, β=90.73(3)°, V=1481.2(9) ų and Z=4 and N-2-(4,6-lutidyl)-N′-2-thiomethoxyphenyl-thiourea, 4,6LutTu2SMe, monoclinic, P2₁/c, a=11.621(1), b=9.324(1), c=14.604(1) Å, β=96.378(4)°, V=1572.4(2) ų and Z=4. Comparisons with other N-2-pyridyl-N′-arylthioureas having substituents in the 2-position of the aryl ring are included.     

The adsorption, CMC determination and corrosion inhibition of some N-alkyl quaternary ammonium salts on carbon steel surface in 2 M H2SO4

Electrochemical measurements were performed to investigate the effectiveness of cationic surfactants of the N-alkyl quaternary ammonium salt type, i.e. myristyltrimethylammonium chloride (MTACl), cetyldimethylbenzylammonium chloride (CDBACl), and trioctylmethylammonium chloride (TOMACl), as corrosion inhibitors for type X4Cr13 ferritic stainless steel in 2 M H₂SO₄ solution. Potentiodynamic polarization measurements showed that these surfactants hinder both anodic and cathodic processes, i.e. act as mixed-type inhibitors. It was found that the adsorption of the N-alkyl ammonium ion in 2 M H₂SO₄ solution follows the Langmuir adsorption isotherm. Plots of log [θ/(1 − θ)] versus log c_inh yielded straight lines with a slope, which changed drastically at the critical micelle concentration (CMC) of the surfactants studied. Accordingly, the CMC could be accurately determined from these measurements. The calculated values of the free energy of adsorption ΔG_ads are, in cases when the charge on the metal surface is negative with respect to the PZC, relatively high what is characteristically for the chemisorption. On the other hand, for positive metal surfaces it is assumed that SO₄²⁻ anions are adsorbed first, so the cationic species would be limited by the surface concentration of anions. Accordingly ΔG_ads values were lower in this case and the adsorption is due to merely electrostatic attraction, which is characteristically of physisorption.     

Structural, spectral and thermal studies of N-2-(4-picolyl)- and N-2-(6-picolyl)-N′-(2-chlorophenyl)thioureas and N-2-(6-picolyl)-N′-(2-bromophenyl)thiourea

N-2-(4-picolyl)-N′-2-chlorophenylthiourea, 4PicTu2Cl, monoclinic, P2₁/c, a=10.068(5), b=11.715(2), β=96.88(4)°, and Z=4; N-2-(6-picolyl)-N′-2-chlorophenylthiourea, 6PicTu2Cl, triclinic, P-1, a=7.4250(8), b=7.5690(16), c=12.664(3) Å, =105.706(17), β=103.181(13), γ=90.063(13)°, V=665.6(2) ų and Z=2 and N-2-(6-picolyl)-N′-2-bromophenylthiourea, 6PicTu2Br, triclinic, P-1, a=7.512(4), b=7.535(6), c=12.575(4) Å, a=103.14(3), β=105.67(3), γ=90.28(4)°, V=665.7(2) ų and Z=2. The intramolecular hydrogen bonding between N′H and the pyridine nitrogen and intermolecular hydrogen bonding involving the thione sulfur and the NH hydrogen, as well as the planarity of the molecules, are affected by the position of the methyl substituent on the pyridine ring. The enthalpies of fusion and melting points of these thioureas are also affected. ¹H NMR studies in CDCl₃ show the NH′ hydrogen resonance considerably downfield from other resonances in their spectra.     

Electronic structures of carbazole and its derivatives: A semi-empirical study on the substitution effects of carbazole

The electronic structures of carbazole, N-phenylcarbazole (NPC), cyanophenylcarbazole (CPC) and N-ethylcarbazole (NEC) have been calculated using the quantum chemical semi-empirical MINDO/3 method. In this paper, electronic ground states and first singlet excited states of the systems mentioned were investigated. It is observed that the excitation energy of carbazole based on the calculated difference in heats of formation agrees quite well with experimental data obtained from supersonic expansion studies. Calculated energy levels of molecular orbitals and their graphical forms are used qualitatively in elucidating the S₀ → S₁ excitation electronic origin red shifts observed in carbazole derivatives with respect to the electronic origin of the parent carbazole. It is noted that the red shifts are not just a result of the destabilization of the HOMO of carbazole but are also determined by the nature of the substituting moieties. It is also observed that the LUMO of CPC is not derived from the parent carbazole which partially explains the difference in electronic behaviour as compared with the other derivatives.     

[2-(N,N-Dimethylaminomethyl)ferrocenyl] as a ligand towards mercury

The diorganomercurial bis[2-(N,N-dimethylaminomethyl)ferrocenyl]mercury(II), (FcN)₂Hg (3), can be obtained by the symmetrisation of the heteroleptic (FcN)HgCl (2) with Na₂S₂O₃ or in the transmetallation reaction of 2 with (FcN)Li. By crystallisation only the crystals of rac-(FcN)₂Hg were obtained. X-ray diffraction analysis revealed linear coordinated mercury atom with two η¹-bonded FcN ligands. Additionally, weak chelate interactions exist between mercury and nitrogen atoms of the ---CH₂NMe₂ side chains. According to the ¹H-NMR findings, these interactions are not preserved in solution. Diorganomercurial 3 appears in solution as a mixture of two diastereomers with rac/meso-(FcN)₂Hg ratio of 1:1. This diastereomeric ratio in solution remains constant within a wide temperature range and in different solvents. The NMR spectroscopic data of the heteroleptic organomercurials [(FcN)HgCl]₂·H₂O (1) and (FcN)HgCl (2) indicate the chelate-free structure of this compounds in solution within the studied temperature interval (−80 to 90 °C).     

Ab initio study of 1,1-(methylphosphinylidene) bis(methanamine) and vibrational assignment of its N,N′-coordinated Pt(II) and Pd(II) chloro complexes

Infrared and Raman spectra of 1,1-(methylphosphinylidene) bis(methanamine) [mpbm, (CH₃)PO(CH₂NH₂)₂] and its N,N′-coordinated Pt(II) and Pd(II) have been studied in the 4000–200 cm⁻¹ frequency range. Ab initio calculations have been carried out for different conformations of the mpbm at HF/6-31G* level of the theory from which structural parameters, conformational stability and predicted infrared and Raman spectra have been obtained. A complete vibrational assignment of the lowest energy conformer, tttg⁻, as well as of its N,N′-coordinated Pt(II) and Pd(II) chloro-complexes was done on the basis of the calculated frequencies, relative infrared intensities, Raman activities and potential energy distribution (PED). The theoretical predictions are compared with the experimental results where appropriate.     

Kinetic study of gas-phase Lu(D3/2) with O2, N2O and CO2

The second-order rate constants of gas-phase Lu(²D_3/2) with O₂, N₂O and CO₂ from 348 to 573 K are reported. In all cases, the reactions are relatively fast with small barriers. The disappearance rates are independent of total pressure indicating bimolecular abstraction processes. The bimolecular rate constants (in molecule⁻¹ cm³ s⁻¹) are described in Arrhenius form by k(O₂)=(2.3±0.4)×10⁻¹⁰exp(−3.1±0.7 kJmol⁻¹/RT), k(N₂O)=(2.2±0.4)×10⁻¹⁰exp(−7.1±0.8 kJmol⁻¹/RT), k(CO₂)=(2.0±0.6)×10⁻¹⁰exp(−7.6±1.3 kJmol⁻¹/RT), where the uncertainties are ±2σ.