α-Fluoroalkylation of carbonyl compounds mediated by a highly reactive alkyl-rhodium complex

Treatment of silyl enol ethers of various carbonyl compounds with Et₂Zn and fluoroalkyl halides (R_f-X) in the presence of RhCl(PPh₃)₃ in DME gave the corresponding α-R_f carbonyl compounds. A highly reactive alkyl-rhodium complex which was derived from RhCl(PPh₃)₃ and Et₂Zn must be crucial in this reaction by accelerating the reaction rate and improving the yields dramatically. This reaction overcomes difficulties on the synthesis of α-R_f carbonyl compounds due to inverse polarization of R_f-X.     

1,3-Dipolar cycloaddition of diazoacetate compounds to terminal alkynes promoted by Zn(OTf)2: an efficient way to the preparation of pyrazoles

A series of pyrazoles were prepared in good yields via 1,3-dipolar cycloaddition of diazoacetate compounds to terminal alkynes promoted by Zn(OTf)₂ under mild conditions. It was supposed that the reaction was through the intermediate of Zn alkynilide.     

Morphology-controlled synthesis of nanostructured zinc hydroxide fluoride via a microwave-assisted ionic liquid route

Zinc hydroxide fluoride (Zn(OH)F) with multiform morphologies such as flower-like particles, pumpkin-like aggregates, and hollow orange-like aggregates are prepared by a microwave-assisted ionic liquid method. During synthesis, microwave irradiation accelerates the reaction rate and shortens the reaction time. 1-Butyl-3-methylimidazolium tetrafluoroborate ([Bmim][BF₄]) or 1-2-hydroxylethyl-3-methylimidazolium tetrafluoroborate ([C₂OHmim][BF₄]) is used as both reactant and template. Experimental results indicate that the morphology evolution of Zn(OH)F is mainly controlled by the concentration of zinc acetate solution. A possible mechanism underlying the formation of nanostructured Zn(OH)F with diverse morphologies is proposed. Furthermore, nanoporous ZnO is obtained by the thermal decomposition of as-prepared Zn(OH)F in air, and the morphology is well retained.     

Coordination polymers derived from gallium and zinc metal–metal bonded species

The reaction of (dpp-bian)Ga–Zn(dpp-bian) (dpp-bian is 1,2-bis[(2,6-diisopropylphenyl)imino]acenaphthene) with 1,3-di(4-pyridyl)propane results in 1D coordination polymer [(dpp-bian)Ga–Zn(dpp-bian)(μ²-1,3-Py₂(CH₂)₃)]_n with the retained Ga–Zn bond. In contrast, the coordination of 1,3-di(4-pyridyl)propane to Zn atoms in the (dpp-bian)Zn–Zn(dpp-bian) complex induces the cleavage of the Zn–Zn bond which is accompanied by reduction of dpp-bian radical anions to dianions. The reaction product represents 1D coordination polymer [{(dpp-bian)Zn}(μ²-1,3-Py₂(CH₂)₃)]_n.     

Insights into the Relationship of Catalytic Activity and Structure: A Comparison Study of Three Carbonic Anhydrase Mimics

Density functional theory (DFT) calculations were used to study the mechanism of CO₂ hydrolysis by Zn‐(1,5,9‐triazacyclododecane) and Zn‐cyclam and evaluate the associated thermodynamic and kinetic parameters. Microkinetic models were then built based on the kinetics and thermodynamics derived from first principles. Both catalysts showed very similar behavior to Zn‐cyclen, which we have reported previously, but with multiple distinctions. The intrinsic reaction rate constants for Zn‐(1,5,9‐triazacyclododecane) and Zn‐cyclam were calculated to be 2693 and 4623 M^?1 s^?1, respectively, which is in reasonable agreement with experimental values reported or estimated. The CO₂ adsorption step was found to be a rate‐limiting step for all three catalysts. Zn‐cyclam has the lowest barrier for this step due to the highest pK_a or nucleophilicity of the Zn‐OH^? form, and_, therefore, the highest intrinsic activity. However, the observed reaction rate constant also depends on the availability of the catalyst. The decrease in the observed reaction rate constant over 0–12 ms was ascribed to the decrease in the concentration of the catalytic form, Zn‐OH^?, which was primarily converted to Zn‐HCO₃^?. The reaction rate constant of Zn‐cyclam dropped much faster than those of Zn‐cyclen and Zn‐(1,5,9‐triazacyclododecane) due to lower energy of the Zn‐HCO₃^? form. The conversion of CO₂ at 1000 ms as a function of pH was calculated to compare the relative activity of these catalysts, and Zn‐cyclen was found to be the best catalyst.     

Thermally latent reaction of hemiacetal ester with epoxide catalyzed by recyclable polymeric catalyst consisting of salen‐zinc complex and polyurethane main chain

This article describes the synthesis of and catalysis with a polymeric catalyst (Zn/ 1_NHCOO ) carrying salen‐zinc complex structure in the main chain prepared from polyaddition of zinc/bis(4‐hydroxy)salicylidene‐1,2‐diiminoethane and 4,4′‐diphenylmethane diisocyanate. Poly(Zn/ 1_NHCOO ) promoted the reaction of glycidyl phenyl ether (2) with 1‐propoxyethyl‐2‐ethylhexanoate (3) only at moderately elevated temperatures. Poly(Zn/ 1_NHCOO ) can be recycled by simple filtration from the reaction mixtures, and the recycled polymer is as active as the freshly prepared one. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 3673–3681, 2008     

Electrochemical studies on Zn deposition and dissolution in sulphate electrolyte

The electrochemical deposition and dissolution of Zn on Pt electrode in sulphate electrolyte was investigated by electrochemical methods in an attempt to contribute to the better understanding of the more complex Zn–Cr alloy electrodeposition process. A decrease of the Zn electrolyte pH (from 5.4 to 1.0) so as to minimise/avoid the formation of hydroxo-products of Cr in the electrolyte for deposition of alloy coatings decreases the current efficiency for the Zn reaction, but the rate of the cathode reaction increases significantly due to intense hydrogen evolution. The results of the investigations in Zn electrolytes with pH 1.0–1.6 indicate that Zn bulk deposition is preceded by hydrogen evolution, stepwise Zn underpotential deposition (UPD) and formation of a Zn–Pt alloy. Hydrogen evolution from H₂O starts in the potential range of Zn bulk deposition. Data obtained from the electrochemical quartz crystal microbalance (EQCM) measurements support the assumption that electrochemical deposition of Zn proceeds at potentials more positive than the reversible potential of Zn. Anodic potentiodynamic curves for galvanostatically and potentiostatically deposited Zn layers provide indirect evidence about the dissolution of Zn from an alloy with the Pt substrate. The presumed potential of co-deposition of Cr (−1.9 V vs. Hg/Hg₂SO₄) is reached at a current density of about 300 mA cm⁻².     

A new method for the stereoselective construction of angular methyl group of fuzed cyclic ethers

A convenient method for the stereoselective construction of angular methyl group of fuzed cyclic ethers is described. Reactions of mixed thioacetals with Me₂Zn/Zn(OTf)₂ afforded the corresponding methylated products in good yields. Various protective groups such as MOM ether, benzylidene acetal, TBS ether, and pivaloyl group were stable under the reaction conditions.     

An efficient synthesis of β-amino esters via Zn(OTf)2-catalyzed Mannich-type reaction

A Zn(OTf)₂-catalyzed Mannich-type reaction of the electron-deficient aromatic amines with the electron-deficient aromatic aldehydes and diethyl malonic ester was described. This three-component reaction afforded the corresponding β-amino esters in good yields.     

Role of Ligand in the Selective Production of Hydrogen from Formic Acid Catalysed by the Mononuclear Cationic Zinc Complexes [(L)Zn(H)]+ (L=tpy,phen, and bpy)

A series of zinc-based catalysts was evaluated for their efficiency in decomposing formic acid into molecular hydrogen and carbon dioxide in the gas phase using quadrupole ion trap mass spectrometry experiments. The effectiveness of the catalysts in the series [(L)Zn(H)]⁺, where L=2,2′:6′,2′′-terpyridine (tpy), 1,10-phenanthroline (phen) or 2,2′-bipyrydine (bpy), was found to depend on the ligand used, which turned out to be fundamental in tuning the catalytic properties of the zinc complex. Specifically, [(tpy)Zn(H)]⁺ displayed the fastest reaction with formic acid proceeding by dehydrogenation to produce the zinc formate complex [(tpy)Zn(O₂CH)]⁺ and H₂. The catalysts [(L)Zn(H)]⁺ are reformed by decarboxylating the zinc formate complexes [(L)Zn(O₂CH)]⁺ by collision-induced dissociation, which is the only reaction channel for each of the ligands used. The decarboxylation reaction was found to be reversible, since the zinc hydride complexes [(L)Zn(H)]⁺ react with carbon dioxide yielding the zinc formate complex. This reaction was again substantially faster for L=tpy than L=phen or bpy. The energetics and mechanisms of these processes were modelled using several levels of density functional theory (DFT) calculations. Experimental results are fully supported by the computational predictions.     

Palladium catalyzed synthesis of aryl thiols: sodium thiosulfate as a cheap and nontoxic mercapto surrogate

A Pd-catalyzed coupling reaction of ArBr/ArCl/ArOTf with sodium thiosulfate takes place in presence of Cs₂CO₃ at 80 °C. The reaction mixture is directly treated with Zn/HCl to afford aryl thiols in good to excellent yields.     

Structure of reaction products of hydrous and anhydrous zinc acetates with 1,10-phenanthroline

A reaction of aqueous zinc acetate with 1,10-phenanthroline produces the ionic complex [(Phen)₂Zn(OOCMe)](OOCMe) · 5H₂O. A similar reaction of “anhydrous zinc acetate” [Zn₇(μ₄-O)₂(μ-OOCMe)₁₀][η-OC(Me)OHNEt₃]₂ in benzene yields a precipitate, which is recrystallized from acetonitrile into trinuclear (Phen)₂Zn₃(μ-OOCMe)₆; and the reaction in acetonitrile yields mononuclear (Phen)Zn(OOCMe)₂ · MeCN. These complexes have been characterized by single-crystal X-ray diffraction.     

An unexpected ethyl transfer reaction between Et2Zn and DI(t-Butyl)-glyoxaldiimine (t-BuDAB). Studies of the persistent [EtZn(t-BuDAB)] radical which is in equilibrium with its C---C coupled dimer

Whereas p-Tol₂Zn reacts with t-BuN=CHCH=N-t-Bu (t-BuDAB) to give a stable complex [p-Tol₂Zn(t-BuDAB)], Et₂Zn gives EtZ -(t-Bu) via intramolecular ethyl transfer in the unstable Et₂Zn(t-BuDAB) complex. In solution the stable persistent organozinc radical EtZn(t-BuDAB), which is formed in trace amounts in the Et₂Zn/t-BuDAB reaction, is in equilibrium with its stable C---C coupled dimer [EtZn-t-BuN=CH(t-BuN)CH]₂. The dimer can be prepared in quantitative yield by the reaction of (EtZnCl)₄ with K(t-BuDAB).     

In situ kinetic studies of the trifluoromethylation of caffeine with Zn(SO2CF3)2

In situ monitoring of the trifluoromethylation of caffeine using Zn(SO₂CF₃)₂ provides mechanistic insight into this important reaction. The concentration dependences of each of the reagents are probed, along with the effect of various additives. The kinetic profile is characterized by a rapid initial regime followed by a period of slower rate. Increasing the concentration of the Zn reagent extends the initial rapid period to higher conversions. Neither the caffeine concentration nor the concentration of the oxidant has a strong effect on the reaction rate. A multiple aliquot method is introduced to help deconvolute factors associated with each rate regime.     

Synthesis and characterization of binuclear Zn(II)–cyclen complexes bridged by α,ω-bis(4-methylphenoxy) alkanes

A series of novel α,ω-bis(4-methylphenoxy) alkane functionalized cyclen ligands were synthesized by the nucleophilic substitution reaction of 1,4,7-tris(tert-butyloxycarbonyl)-1,4,7,10-tetraazacyclododecane and α,ω-bis(4-bromomethylphenoxy) alkanes. The corresponding dimeric Zn(II)–cyclen complexes were obtained by reaction of these ligands with Zn(ClO₄)₂·6H₂O. Ligands and complexes were characterized by FT-IR, ¹H NMR, and elemental analysis.     

Proton-Reservoir Hydrogel Electrolyte for Long-Term Cycling Zn/PANI Batteries in Wide Temperature Range

Advanced aqueous batteries are promising for next generation flexible devices owing to the high safety, yet still requiring better cycling stability and high capacities in wide temperature range. Herein, a polymeric acid hydrogel electrolyte (PAGE) with 3 M Zn(ClO₄)₂ was fabricated for high performance Zn/polyaniline (PANI) batteries. With PAGE, even at −35 °C the Zn/Zn symmetrical battery can keep stable for more than 1 500 h under 2 mA cm⁻², and the Zn/PANI battery can provide ultra-high stable specific capacity of 79.6 mAh g⁻¹ for more than 70 000 cycles at 15 A g⁻¹. This can be mainly ascribed to the −SO₃⁻H⁺ function group in PAGE. It can generate constant protons and guide the (002) plane formation to accelerate the PANI redox reaction kinetics, increase the specific capacity, and suppress the side reaction and dendrites. This proton-supplying strategy by polymeric acid hydrogel may further propel the development of high performance aqueous batteries.     

Direct Enantioselective Vinylogous Mannich Reaction of Ketimines with γ‐Butenolide by Using Cinchona Alkaloid Amide/Zinc(II) Catalysts

A direct enantioselective vinylogous Mannich reaction of ketimines with γ‐butenolide has been developed. Good yields and enantioselectivities were observed for the reaction of various ketimines by using a cinchona alkaloid amide/Zn(OTf)₂ catalyst and Et₃N. Both enantiomers of the products could be obtained by using pseudoenantiomeric chiral catalysts.     

Photo-excited Oxygen Reduction and Oxygen Evolution Reactions Enable a High-Performance Zn–Air Battery

The storage of solar energy in battery systems is pivotal for a sustainable society, which faces many challenges. Herein, a Zn–air battery is constructed with two cathodes of poly(1,4-di(2-thienyl))benzene (PDTB) and TiO₂ grown on carbon papers to sandwich a Zn anode. The PDTB cathode is illuminated in a discharging process, in which photoelectrons are excited into the conduction band of PDTB to promote oxygen reduction reaction (ORR) and raise the output voltage. In a reverse process, holes in the valence band of the illuminated TiO₂ cathode are driven for the oxygen evolution reaction (OER) by an applied voltage. A record-high discharge voltage of 1.90 V and an unprecedented low charge voltage of 0.59 V are achieved in the photo-involved Zn–air battery, regardless of the equilibrium voltage. This work offers an innovative pathway for photo-energy utilization in rechargeable batteries.     

Synthesis of amides from imines using Et3SiH/Zn system

A simple and efficient approach for the synthesis of amides by the reaction of imines and acyl chlorides in the presence of Et₃SiH/Zn system in THF at ambient temperature is reported. Mild reaction conditions, good yields of products, short reaction time and operational simplicity are the advantages of this procedure. Copyright © 2012 John Wiley & Sons, Ltd.     

Synthesis of trans‐Disubstituted Alkenes by Cobalt‐Catalyzed Reductive Coupling of Terminal Alkynes with Activated Alkenes

A cobalt‐catalyzed reductive coupling of terminal alkynes, RC?CH, with activated alkenes, R′CH?CH₂, in the presence of zinc and water to give functionalized trans‐disubstituted alkenes, RCH?CHCH₂CH₂R′, is described. A variety of aromatic terminal alkynes underwent reductive coupling with activated alkenes including enones, acrylates, acrylonitrile, and vinyl sulfones in the presence of a CoCl₂/P(OMe)₃/Zn catalyst system to afford 1,2‐trans‐disubstituted alkenes with high regio‐ and stereoselectivity. Similarly, aliphatic terminal alkynes also efficiently participated in the coupling reaction with acrylates, enones, and vinyl sulfone, in the presence of the CoCl₂/P(OPh)₃/Zn system providing a mixture of 1,2‐trans‐ and 1,1‐disubstituted functionalized terminal alkene products in high yields. The scope of the reaction was also extended by the coupling of 1,3‐enynes and acetylene gas with alkenes. Furthermore, a phosphine‐free cobalt‐catalyzed reductive coupling of terminal alkynes with enones, affording 1,2‐trans‐disubstituted alkenes as the major products in a high regioisomeric ratio, is demonstrated. In the reactions, less expensive and air‐stable cobalt complexes, a mild reducing agent (Zn) and a simple hydrogen source (water) were used. A possible reaction mechanism involving a cobaltacyclopentene as the key intermediate is proposed.