Long-lived metastable anions of hydrogen halides

We search for narrow resonances in cross-sections for electron collisions with HCl, DCl, HBr and DBr molecules, calculated with the nonlocal resonance model. Narrow resonances corresponding to long-lived metastable states of anionic molecules are indeed found in both elastic and vibrational excitation cross-sections. The largest lifetime τ = 0.11 ms is predicted for HBr⁻ with rotational quantum number J = 20. For HCl we find maximum τ = 0.6 ns for J = 22 and τ = 0.6 μs for J = 33 in DCl. A surprising isotope effect is found for DBr, where the largest lifetime is τ = 1.5μs, i.e., much smaller than for HBr.     

Singlet and triplet state dynamics of charge and hydride transfer reactions of OD (XΣ) with propyne

We report a crossed beam study of the title reactions in the collision energy range from 0.45 to 1.23 eV (43–119 kJ/mol). Both reactions are exoergic and proceed as direct processes on a time scale much less than the rotational period of the transient association complex of approaching reactants. The charge transfer process takes place with zero momentum transfer. Density Functional Theory calculations of the structures of reactive intermediates show that a plausible pathway for hydride transfer involves initial charge transfer on a triplet surface, followed by intersystem crossing to the singlet manifold. This process is followed by rapid hydrogen atom transfer to form an intermediate that dissociates smoothly to products. The kinematics of the heavy + light-heavy mass combination result in mixed energy release at the lowest collision energy, in which both the breaking and forming bonds are extended, while at higher collision energies, the incremental translational energy in the reactants appears preferentially in product translation, consistent with induced repulsive energy release.     

Frozen aryldiazonium chlorides in radical reactions with alkenes and arenes

Frozen aryldiazonium chlorides have been investigated in radical alkene and arene functionalizations. Through freezing at – 84?°C, aryldiazonium chlorides, which otherwise show significant decomposition in aqueous solution after several hours at room temperature, can be stored for at least 20 days. In addition, the slow melting of aryldiazonium-containing ice cubes can serve as an alternative to syringe pumps that are commonly used if a controlled addition of the diazonium salt to the reaction mixture is required.     

Cobalt-catalyzed cross-coupling reactions of alkyl halides with aryl Grignard reagents and their application to sequential radical cyclization/cross-coupling reactions

Reactions of alkyl halides with arylmagnesium bromides in the presence of cobalt(II)(diphosphine) complexes are discussed. Treatment of 1-bromooctane with phenylmagnesium bromide with the aid of a catalytic amount of CoCl₂(dppp) [DPPP=1,3-bis(diphenylphosphino)propane] yielded octylbenzene in good yield. The reaction mechanism would include single electron transfer from an electron-rich cobalt complex to alkyl halide to generate the corresponding alkyl radical. The mechanism was justified by CoCl₂(dppe)-catalyzed [DPPE=1,2-bis(diphenylphosphino)ethane] sequential radical cyclization/cross-coupling reactions of 6-halo-1-hexene derivatives that yielded benzyl-substituted cyclopentane skeletons.     

Synthesis of substituted uracils by the reactions of halouracils with selenium, sulfur, oxygen and nitrogen nucleophiles under focused microwave irradiation

Under microwave irradiation, the nucleophilic substitution reactions of halouracils with selenium, sulfur, oxygen and nitrogen nucleophiles was complete within several minutes with yields up to 99%. The method using microwave irradiation is superior to those conducted under conventional heating processes.     

Synthesis of isoquinolines through the coupling of Fischer carbene complexes with o-alkynylpyridine carbonyl derivatives

The reaction of Fischer carbene complex with o-alkynylpyridine carbonyl derivatives has been investigated. This involves the generation of furo[3,4-c]pyridine as transient intermediates through the coupling of o-alkynylpyridine carbonyl derivatives with carbene complex and subsequent Diels–Alder trapping with suitable dienophiles resulted in the formation of isoquinoline derivatives and the entire sequence can be run in one pot. When an olefinic tether was present, intramolecular Diels–Alder cycloaddition occurred followed by ring opening to yield tricyclic alcohols.     

Interfacial reactions of nickel ion containing multilayers and nickel ultra‐thin films with an interpenetrating polymer network substrate

An interpenetrating polymer network (IPN) substrate was prepared by dip‐pulling a silicon wafer or glass plate into polymer precursors, followed by solidification at room temperature. The nickel ion containing Langmuir–Blodgett (LB) multilayers was subsequently fabricated onto the IPN substrate by a LB technique, and then the nickel ultra‐thin films were deposited by chemical reduction. The interfacial reactions, the metal transformations and the non‐metal bond types during the film formation were detected by the X‐ray photoelectron spectroscopy, atomic force microscope and attenuated total reflection infrared spectroscopy. Copyright © 2011 John Wiley & Sons, Ltd.     

Dimethylzinc-initiated radical reaction of cyclic ethers with arylamines, alkoxyamines, and dialkylhydrazines

Dimethylzinc-initiated radical reaction of THF with arylamines afforded aminoalcohols which were derived from the two molecules of THF and one molecule of an arylamine. The reaction seems to proceed via two-consecutive processes, electrophilic and then nucleophilic reactions of THF-derived species. Alkoxyamines and dialkylhydrazines reacted with electrophilic cyclic ether species to give the corresponding oximes and hydrazones of ω-hydroxyalkanal.     

Preparation of polythioamides from dialdehydes and diamines with sulfur by the Willgerodt–Kindler type reaction

Willgerodt–Kindler type reactions of dialdehydes and diamines in the presence of sulfur were investigated for preparation of polythioamides. The one‐pot, three‐component polycondensation afforded various polythioamides in moderate to good yields. The appropriate reaction conditions were examined for the separate monomers. The results led us to the proposed mechanism for the polycondensation including formation of the intermediate Schiff base polymers followed by the successive nucleophilic attack of polysulfide anions to the azomethine units to give the thioamide groups. Structure, solubility, and thermal properties of the polythioamides were also compared with those of analogous polyamides. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 3739–3750, 2001     

Synthesis of a poly(vinyl ether) containing a benzocyclobutene moiety and its reaction with dienophiles

1‐Benzocyclobutenyl vinyl ether (1) was easily prepared by the elimination reaction of hydrogen bromide from 1‐benzocyclobutenyl 1‐bromoethyl ether obtained by 1‐bromobenzocyclobutene and ethylene glycol via two steps in a good yield. Cationic polymerizations of 1 was carried out at −78°C for 2 h in toluene in the presence of BF₃OEt₂ as an initiator to give quantitatively the corresponding polymers (2) as white solids. As a model reaction of the polymer reaction of 2 with dienophiles, the Diels–Alder reactions of 1‐methoxybenzocyclobutene with maleic anhydride (MA) in toluene at 100–140°C for 3 h were carried out to obtain the corresponding Diels–Alder adduct quantitatively at 140°C. The polymer reactions of 2 with MA and N‐phenylmaleimide (MI) in toluene were carried out to yield the corresponding Diels–Alder adduct polymers in good yields. The degree of introduction of the dienophile could be controlled by temperature, and the unreacted benzocyclobutene moiety could further react with another benzocyclobutene moiety or dienophile. The properties (solubilities, T_g, and temperature of 10% weight loss) of the polymers obtained from the polymer reaction were quite different from those of 2. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 59–67, 1999     

Experimental and theoretical investigation of NMR 2JHH coupling constant on six-membered ring systems containing oxygen or sulfur atoms

Theoretical and experimental 2JHH coupling constants for six-membered rings containing oxygen or sulfur atoms were studied to investigate whether the 2JHH coupling constant can be used for stereoelectronic studies in heterocyclohexanes, instead of 1JCH, because it is well known that experimental measurements of 2JHH coupling constants at low temperature are much easier to determine than the corresponding 1JCH couplings. For all compounds studied here, the 2JHH coupling constants are affected by sigma*C-H antibonding occupancy together with bond angle effects. For cyclohexane and oxygen-containing compounds, the influence on the geminal coupling for Hax-C2-Heq and for X1-C2-X3 (X=O and C), bond angles are more pronounced than for the sulfur derivatives.     

Gas-phase combination reactions of SF4 and SF5 with F in plasmas of SF6

Reactions of both SF₄ and SF₅ with F have been studied at 295 K in a gas-flow reactor sampled by a mass spectrometer. The rate coefficient for the combination reaction of F with SF₄ to produce SF₅ was found to increase from (0.9 to 3.0)×10^–12 cm³ s^–1 when the helium bath gas number density was increased from (2 to 26)×10¹⁶ cm^–3. The values obtained here are three orders of magnitude higher than a recent estimate of the high-pressure value based on the modelling of photochemical studies. The experimental results have been compared with RRKM and master equation calculations in which a simplified Gorin model has been used to determine the structure of the transition state. These calculations show that reasonable agreement can be obtained between the experimental data and the calculation if a small (2 KJ/mol) activation energy is assumed. The rate coefficient for the reaction between SF₅ and F to produce SF₆ was found to be independent of helium bath gas number density within the range given above. The value obtained for the rate coefficient was 9×10^–12 cm³ s^–1 with an uncertainty of a factor of 2. This value is close to that of 1×10^–11 cm³ s^–1 computed from the simplified Gorin model and to the value of 1.7×10^–11 cm³ s^–1 deduced from modelling of photochemical experiments.     

Synthesis,characterization and catalytic activity in Suzuki–Miyaura coupling of palladacycle complexes with n‐butyl‐substituted N‐heterocyclic carbene ligands

A series of monomeric palladacycle complexes bearing n‐butyl‐substituted N‐heterocyclic carbenes, namely [Pd(NHC)X(dmba)] (dmba: dimethylbenzylamine and [Pd(NHC)X(ppy)]; NHC: 1‐n‐butyl‐3‐substituted benzylimidazol‐2‐ylidene; ppy: 2‐phenylpyridine), were prepared either by transmetallation from the corresponding silver carbene complexes or by the reaction of the corresponding acetate‐bridged palladacycle dimer with N‐heterocyclic carbene ligands in high yields. The palladium(II) complexes were characterized using elemental analyses, APCI‐MS, ¹H NMR and ¹³C NMR spectroscopies. These complexes are efficient in the Suzuki–Miyaura coupling reaction between phenylboronic acid and aryl bromides.     

Synthesis and characterization of copper(II) dithiocarbamate complexes involving pyrrole and ferrocenyl moieties and their utility for sensing anions and preparation of copper sulfide and copper–iron sulfide nanoparticles

Bis(N‐(pyrrol‐2‐ylmethyl)‐N‐butyldithiocarbamato‐S,S′)copper(II) ( 1 ), bis(N‐(pyrrol‐2‐ylmethyl)‐N‐(2‐phenylethyl)dithiocarbamato‐S,S′)copper(II) ( 2 ), bis(N‐methylferrocenyl‐N‐(2‐phenylethyl)dithiocarbamato‐S,S′)copper(II) ( 3 ) and bis(N‐furfuryl‐N‐methylferrocenyldithiocarbamato‐S,S′)copper(II) ( 4 ) were prepared and characterized using elemental analysis and infrared and UV–visible spectroscopies. X‐ray diffraction (XRD) studies on 3 show that each copper centre adopts the square planar geometry by the coordination of four sulfur atoms of the metalloligand N‐methylferrocenyl‐N‐(2‐phenylethyl)dithiocarbamate. The Cu? S distances are symmetrical and are in the range 2.293–2.305 Å. The supramolecular architecture in complex 3 is sustained in the solid state by C? H???π, C? H???S, Fe???Fe and H???H interactions. Density functional theory calculations were carried out for 3 . Anion (F^?, Cl^?, Br^? and I^?) binding studies with complex 1 were performed using cyclic voltammetry. Copper sulfide, copper–iron sulfide‐ 1 and copper–iron sulfide‐ 2 nanoparticles were prepared from complexes 2 , 3 and 4 , respectively, and they were characterized using powder XRD, transmission electron microscopy (TEM) and energy‐dispersive X‐ray, UV–visible, photoluminescence and infrared spectroscopies. TEM images of copper–iron sulfide‐ 1 and copper–iron sulfide‐ 2 reveal that the particles are spherical and oval shaped, respectively. Photocatalytic activities of as‐prepared nanoparticles were studied by decolourization of methylene blue and rhodamine‐B under UV light. It was found that copper–iron sulfide degrades methylene blue and rhodamine‐B much better than does copper sulfide.     

Preparation of ABC miktoarm star terpolymer containing poly(ethylene glycol), polystyrene,and poly(tert‐butylacrylate) arms by combining diels–alder reaction,atom transfer radical,and stable free radical polymerization routes

The ABC type miktoarm star terpolymer was prepared utilizing “core‐in” and “core‐out” methods via combination of Diels–Alder reaction (DA), stable free radical polymerization (SFRP), and atom transfer radical polymerization (ATRP). First, in DA reaction, poly(ethylene glycol)‐maleimide (PEG‐maleimide) precursor was reacted with succinic acid anthracen‐9‐ylmethyl ester 3‐(2‐bromo‐2‐methyl‐propionyloxy)‐2‐methyl‐2‐[2‐phenyl‐2‐(2,2,6,6‐tetramethyl‐piperidin‐1‐yloxy)‐ethoxy‐carbonyl]‐propyl ester, 8 , to give DA adduct, 9 , which has appropriate functional groups for SFRP and ATRP. Second, a previously obtained 9 was used as a macroinitiator for SFRP of styrene at 125 °C. As a third step, this PEG‐polystyrene (PEG‐PSt) precursor with a bromine functionality in the core was employed as a macroinitiator for ATRP of tert‐butylacrylate (tBA) in the presence of Cu(I)Br and pentamethyldiethylenetriamine at 80 °C to give ABC type miktoarm star terpolymer (PEG‐PSt‐PtBA) with controlled molecular weight and low polydispersity (M_w/M_n < 1.27). The obtained polymers were characterized by gel permeation chromatography and ¹H NMR. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 499–509, 2006     

Biochar as heterogeneous support for immobilization of Pd as efficient and reusable biocatalyst in C–C coupling reactions

Biochar is a stable and carbon‐rich solid which has a high density of carbonyl, hydroxyl and carboxylic acid functional groups on its surface. In this work, the surface of biochar nanoparticles (BNPs) was modified with 3‐choloropropyltrimtoxysilane and further 2‐(thiophen‐2‐yl)‐1H‐benzo[d]imidazole was anchored on its surface. Then, palladium nanoparticles were fabricated on the surface of the modified BNPs and further the catalytic application was studied as recyclable biocatalyst in carbon–carbon coupling reactions such as Suzuki–Miyaura and Heck–Mizoroki cross‐coupling reactions. The structure of the catalyst was characterized using scanning electron microscopy, transmission electron microscopy, energy‐dispersive X‐ray spectroscopy, thermogravimetric analysis, X‐ray diffraction and atomic absorption spectroscopy. The catalyst can be reused several times without a decrease in its catalytic efficiency. In addition to the several advantages reported, application of biochar as catalyst support for the first time is a major novelty of the present work.     

Synthesis of internal alkynes via one-pot palladium-catalyzed and dehydrobromination reactions of 1,1-dibromo-1-alkenes

Tandem palladium-catalyzed cross-coupling of alkyl, alkenyl, alkynyl, aryl, and heteroaryl 2-substituted 1,1-dibromo-1-alkenes with aryl or heteroaryl boronic acids or borate esters and dehydrobromination of the intermediate coupled products afforded internal alkynes in moderate to good yields (up to 89%). The synthesis has been carried out in a one-pot process and in a two-step sequence according to the nature of the starting 1,1-dibromoalkenes. The reported protocol is compatible with the presence in the 1,1-dibromo-1-alkene molecule of additional reactive halogen–carbon bonds, thus allowing to build up more complex alkyne derivatives.     

Gas-phase reactions in plasmas of SF6 with O2: Reactions of F with SOF2 and SO2 and reactions of O with SOF2

The plasma chemistry of SF₆/O₂ mixtures is particularly complicated because of the large number of possible reactions. Over a wide range of conditions, products including SF₄, SOF₄, SOF₂, and SO₂F₂ can be formed but thre is considerable uncertainty about the major reactions which contribute to the formation of these species. In this work reactions of oxygen atoms with SOF₂ and fluorine atoms with SOF₂ and SO₂ have been studied in order to determine the principal sources of SO₂F₂ in these plasmas. Reactions were studied at 295 K in a gas flow reactor sampled by a mass spectrometer. No reaction could be detected between oxygen atoms and SOF₂, which for the conditions employed, means that the upper limit for the reaction rate coefficient is 1×10^–14 cm³ sec^–1. The reaction of fluorine atoms with SOF₂ was studied with the helium bath gas number density ranging from 3.1×10¹⁶ to 2.0×10¹⁷ cm^–3. Within this range the rate coefficient increased with increasing [He] from (4.1 to 10.8)×10^–14 cm³ sec^–1. SO₂ was found to react with fluorine atoms with a rate coefficient which appeared to be independent of the helium bath gas number density over the range given above. The possibility that this reaction occurred entirely on the walls of the reactor is discussed.