CoBr2 Research Articles

Structural phase transition and optical properties of zero-dimensional cobalt bromide hybrid material

Zero-Dimensional (0D) metal halide materials have recently emerged as a class of potential optoelectronic materials because of the structural diversity and superior photophysical properties. Here we report a 0D cobalt bromide hybrid material, [Br(CH2)3NH3]2CoBr4 (BPA-CoBr4, BPA=Br(CH2)3NH3, 3-Bromopropylamine), in which the isolated metal halide tetrahedron (CoBr42-) is completely separated each other and surrounded by the organic ligand Br(CH2)3NH3+. Differential scanning calorimetry (DSC) measurements exhibit BPA-CoBr4 undergoes a first-order structural phase transition, as clearly visible to a pair of weak peaks at 340 K (heating) and 317 K (cooling). Single crystal X-ray diffractions were carried out at 293 K and 360 K to explain the phase transformation mechanism, indicating it is an isostructural order–disorder type. The crystal structures which both crystalize in a monoclinic P21/c crystal symmetry and the most distinct difference between room-temperature and high-temperature structures is the order–disorder transition of the 3-Bromopropylamine, which is the driving force of the phase transition. The UV–vis absorption spectra reveal that BPA-CoBr4 has a steep absorption edge at 280 nm corresponding to photo energy of 4.4 eV. The density functional theory (DFT) calculations were performed to study the electronic structure with narrower indirect bandgap 3.9 eV which is lower than the experimental values. PDOS plots show that the electronic states of Co-d and Br-p orbitals are mainly contributed for the VBM and CBM of BPA-CoBr4.

Mechanistic Investigations of Phenoxyimine-Cobalt(II)-Catalyzed C(sp2)-C(sp3) Suzuki-Miyaura Cross-Coupling.

The mechanism of phenoxyimine (FI)-cobalt-catalyzed C(sp2)-C(sp3) Suzuki-Miyaura cross-coupling was studied using a combination of kinetic measurements and catalytic and stoichiometric experiments. A series of dimeric (FI)cobalt(II) bromide complexes, [(4-CF3PhFI)CoBr]2, [(4-OMePhFI)CoBr]2, and [(2,6-diiPrPhFI)CoBr]2, were isolated and characterized by 1H and 19F NMR spectroscopies, solution and solid-state magnetic susceptibility, electron paramagnetic resonance (EPR) spectroscopy, X-ray crystallography, and diffusion-ordered NMR spectroscopy (DOSY). One complex, [(4-CF3PhFI)CoBr]2, was explored as a single-component precatalyst for C(sp2)-C(sp3) Suzuki-Miyaura cross-coupling. Addition of potassium methoxide to [(4-CF3PhFI)CoBr]2 generated the corresponding (FI)cobalt(II) methoxide complex as determined by 1H and 19F NMR and EPR spectroscopies. These spectroscopic signatures were used to identify this compound as the resting state during catalytic C(sp2)-C(sp3) coupling. Variable time normalization analysis (VTNA) of in situ catalytic 19F NMR spectroscopic data was used to establish an experimental rate law that was first-order in a (FI)cobalt(II) precatalyst, zeroth-order in the alkyl halide, and first-order in an activated potassium methoxide-aryl boronate complex. These findings are consistent with turnover-limiting transmetalation that occurs prior to activation of the alkyl bromide electrophile. The involvement of boronate intermediates in transmetalation was corroborated by Hammett studies of electronically differentiated aryl boronic esters. Together, a cobalt(II)/cobalt(III) catalytic cycle was proposed that proceeds through a "boronate"-type mechanism.

Cobalt(II) coordination to an N4-acenaphthene-based ligand and its sodium complex.

A new bifunctional N4-ligand was obtained via the condensation reaction of acenaphthenequinone and 2-picolylamine. A peculiarity of this synthesis is the formation of a new intramolecular C-C bond during the reaction. The structure and redox properties of the ligand were studied. The anion-radical form of the ligand was prepared via the chemical reduction of the latter with metallic sodium as well as in situ via its electrochemical reduction in a solution. The sodium salt prepared was structurally characterized using single-crystal X-ray diffraction (XRD). New cobalt complexes with the ligand in neutral and anion-radical forms were synthesized and further studied. As a result, three new homo- and heteroleptic cobalt(II) complexes were obtained, in which the cobalt atom demonstrates different modes of coordination with the ligand. Cobalt(II) complex CoL2 with two monoanionic ligands was prepared by the electrochemical reduction of a related L2CoBr2 complex or by treating cobalt(II) bromide with the sodium salt. XRD was used to study the structures of all cobalt complexes prepared. Magnetic and electron paramagnetic resonance studies were performed: CoII ion states with S = 3/2 and S = 1/2 were found for the complexes. A quantum-chemical study confirmed that the spin density is mainly located at the cobalt center.

Co/Zn Bimetallic Catalysis Enables Enantioselective Alkynylation of Isatins and α-Ketoesters Using Terminal Alkynes.

We present herein a novel cobalt/zinc bimetallic catalysis system for the realization of an efficient and enantioselective alkynylation of isatins and α-ketoesters using terminal alkynes. By using a simple procedure with all commercially available catalysts, including cobalt bromide, a chiral bisphosphine ligand, and zinc triflate, a range of synthetically useful tertiary propargylic alcohols are accessed with high yields and good enantioselectivities. Control reactions showed that this catalytic system proceeds through activation of the terminal alkyne by zinc triflate and a base, transmetalation from zinc to cobalt, and then the enantio-determining alkynylation of ketones.

A new method for the synthesis of 4-aminobenzoic acid – an intermediate for the production of procaine

Procaine is one of the oldest local anesthetics used in medicine. When absorbed and entering the systemic circulation reduces the excitability of peripheral cholinoreactive systems. Has a blocking effect on the autonomic ganglia, reduces smooth muscle spasms, and reduces the excitability of the myocardium and motor areas of the cerebral cortex. It is synthesized by oxidizing 4-nitrotoluene to 4-nitrobenzoic acid, which is subsequently reacted with thionyl chloride, the resulting acid chloride is then esterified with 2-diethylaminoethanol to give nitrocaine. Finally, the nitro group is reduced by hydrogenation over a Raney nickel catalyst. The oxidation stage is characterized by the formation of toxic, difficult to dispose of wastewater, valuable mineral oxidants, or high temperatures and excess pressure, in the case of using oxygen as an oxidant. Therefore, the search for new environmentally friendly and low-temperature methods of obtaining 4-nitrobenzoic acid is an urgent task. The aim of the work is to study the products, conditions, and study kinetics of the reaction of ozone with 4-nitrotoluene in acetic acid solution to develop a new method for the synthesis of 4-nitrobenzoic acid. Materials and methods. The glacial acetic acid qualification “P. F. A.” before use was purified by distillation under vacuum in the presence of potassium permanganate. Salts of metals of qualification “P. F. A.” and potassium bromide qualification “Ch. P.” were used without prior purification. A gas-phase gradient-free catalytic duck reactor was used for kinetic studies. The mixing of gas and liquid phases in the reactor was achieved by shaking the reactor at a speed that allowed it to work in the kinetic region. The kinetics of the reaction was studied by changing the concentration of ozone in the gas phase at the outlet of the reactor by spectrophotometric method on a spectrophotometer “SF-46 LOMO”. Results. The products, conditions, and kinetics of ozone reaction with 4-nitrotoluene were studied. It was shown that at temperatures of 20–90 °C is mainly ozonolysis of the aromatic ring, and the total yield of oxidation products by methyl group does not exceed 24.2 %, among which identified in the early stages of 4-nitrobenzyl alcohol and 4-nitrobenzaldehyde, and at deeper – 4-nitrobenzoic acid. The introduction of cobalt (II) acetate into the catalyst system almost completely was prevented ozonolysis and the main reaction product is 4-nitrobenzoic acid with a yield of 86.5 %. The addition of potassium bromide to the solution reduced the concentration of the catalyst by seven times and increased the reaction rate and yield of 4-nitrobenzoic acid to 95.6 %. Conclusions. A new environmentally friendly, low-temperature method for the synthesis of 4-nitrobenzoic acid by conducting the process of ozonation of 4-nitrotoluene in a solution of glacial acetic acid in the presence of a mixed cobalt bromide catalyst was developed.

Cobalt Bromide-Catalyzed Negishi-Type Cross-Coupling of Amides.

Herein, we describe a novel Negishi-type cross-coupling of amides employing only cobalt bromide salt as the catalyst. This original reaction is highly tolerant to various glutarimide amides as well as organozinc coupling partners. These conditions also allow the performance of the cross-coupling reaction in an eco-compatible solvent such as ethyl acetate on a large scale.

Characterization of Substituted 1,3-Dioxolanes and 1,3-Dioxanes by Gas Chromatography–Mass Spectrometry

Until recently, one of the reasons for the unsatisfactory characterization of alicyclic ketals of aliphatic and alkylaromatic ketones was the absence of any mention of the presence of such compounds in natural samples. Another reason is in the low yields of such ketals on the interaction of ketones and diols under the conditions of conventional acid catalysis. To optimize the synthesis of trace amounts of such ketals, we used cobalt(II) bromide and dimethyl glyoxime as catalysts. The simplest chromatographic parameters, including the difference between the retention indices of the products and the starting compounds (difference in retention indices, DRI), are effective for identifying the target ketals in reaction mixtures. Such combined chromatography–mass spectrometric characteristics as homologous increments of retention indices (iRI) are informative not only for the group identification of analytes (assignment to the corresponding homologous series) and the assessment of their molecular weights (at low-intense signals of molecular ions). They are also useful for the determination of the total number of branches of the sp3-carbon skeleton of molecules (N) using the regression of N ≈ aiRI + b.

Bromination of α‐Diazo Phenylacetate Derivatives Using Cobalt(II) Bromide

AbstractA method for the bromination of α‐diazo phenylacetate derivatives using cobalt(II) bromide is described. This bromination reaction features a short reaction time, broad substrate scope, operational simplicity, acid‐free conditions, and gram‐scalability.magnified image

Cobalt(II)-catalyzed preparation of alkylindium reagents and applications in cross-coupling with aryl halides

The direct insertion of indium powder into alkyl iodides was found to be efficiently catalyzed by a catalytic amount of cobalt(II) bromide (10 mol%). Upon subjection of the thus-formed alkylindium compounds to palladium-catalyzed cross-coupling reactions with a wide range of aryl halides, a series of cross-coupled products could be obtained in moderate to good yields with the tolerance to many important functional groups.

(MeCN)3Co(C2F5)3]: A Versatile Precursor to Cobalt(III) Perfluoroethyl Complexes

The air-stable [fac-(MeCN)3Co(C2F5)3] (1) was prepared through the reaction of cobalt(II) bromide with [Me3Si-C2F5] and AgF. Upon reaction of 1 with wet pyridine, the unexpected product [fac-(H2O)3...

Polymerization of conjugated dienes and olefins promoted by cobalt complexes supported by phosphine oxide ligands

Four cobalt complexes supported by phosphine oxide (P=O) donors (9,9-dimethyl-9H-xanthene-4,5-diyl)bis(diphenylphosphine oxide) cobalt dichloride (Co1), (9,9-dimethyl-9H-xanthene-4,5-diyl)bis(diphenylphosphine oxide) cobalt bromide (Co2), N, N'-(pyridine-2,6-diyl)bis(P,P-di-tert-butylphosphinic amide) cobalt dichloride (Co3) and N, N'-(pyridine-2,6-diyl)bis(P,P-di-tert-butylphosphinic amide) cobalt dichloride (Co4) were prepared and characterized. Their catalyses performances in polymerization of isoprene, butadiene, myrcene as well as MMA and styrene were examined. In combination with AlEt2Cl, Co1 and Co2 are able to convert isoprene to polyisoprene, whereas the activities of Co3 and Co4 are much low. The resultant polyisoprene are mixture of cis-1,4 and 3,4 isomers, whose ratio are not significantly affected by the type of catalysts and polymerization conditions. Isoprene was found to be more active than myrcene, and butadiene in the case of Co1/AlEt2Cl, suggestive of compromised sterical and electronic effect from the alkyl group at 2-positon of monomers. The Co1/AlEt2Cl system is also moderately active in polymerizations of methyl methacrylate and styrene. Therefore, the current catalysts provided dual polymerization reactivities towards conjugated dienes and olefins that are rare in transition metals catalyzed coordinative polymerization.

Cobalt-Catalyzed Alkoxycarbonylation of Epoxides to β-Hydroxyesters.

Herein, we developed a new and practical catalytic system for the carbonylative synthesis of β-hydroxyesters. By using simple, cheap, and air-stable cobalt(II) bromide as the catalyst, combined with pyrazole and catalytic amount of manganese, active cobalt complex can be generated in situ and can catalyze various epoxides to give the corresponding β-hydroxyesters in moderate to excellent yields. Mechanism studies indicate that pyrazole plays a crucial role in this reaction. Moreover, with the addition of the catalytic amount of manganese, the active cobalt catalyst can be regenerated, which provides a possibility for reusing the cobalt catalyst.

In Situ Generated Cobalt Catalyst for the Dehydrogenative Coupling of Alcohols and Amines into Imines

AbstractAn in situ formed cobalt catalyst is developed from cobalt(II)bromide, bis[2‐(diisopropylphosphino)‐4‐methylphenyl]amine and zinc metal. The catalyst mediates the acceptorless dehydrogenative coupling of alcohols and amines into imines with the release of hydrogen gas and the transformation is applied to the synthesis of a variety of imines from different alcohols and amines. The mechanism is investigated with labelled substrates and based on the results a cobalt(I) PNP complex is believed to be the catalytically active species which abstracts hydrogen gas from the alcohol through a metal ligand bifunctional pathway.

Cobalt and zinc halide complexes of 4-chloro and 4-methylaniline: Syntheses, structures and magnetic behavior

A family of cobalt(II) and zinc(II) compounds with the general formula (4-subC6H4NH2)2MX2, (M = Co, Zn; X = Cl, Br; sub = CH3, Cl) has been prepared and the compounds characterized by single-crystal X-ray diffraction. The eight compounds crystallize in the monoclinic space group I2/a and are isocoordinate, but show different crystal packing for the 4-methyl and 4-chloroaniline complexes as a result of halogen bonding in the 4-chloroaniline family. The cobalt complexes have also been studied via variable temperature magnetic susceptibility measurements. All four Co(II) compounds exhibit antiferromagnetic exchange (maxima in χ are observed) and have been fitted with a 1D-chain model (cobalt chloride complexes, J ∼ −3 K) or a 2D-model (cobalt bromide complexes, J ∼ −4 K). Analysis of potential superexchange pathways is provided.

Sequential Organozinc Formation and Negishi Cross‐Coupling of Amides Catalysed by Cobalt Salt

AbstractHerein, a cobalt‐catalysed Negishi‐type cross‐coupling of amide derivatives is described. Apart from being the first example of cobalt‐catalysed Negishi‐type coupling of amides, the process described employs a unique, simple, and cheap catalytic system to perform both the organozinc formation and the Negishi‐type coupling. Indeed, the same cobalt(II) bromide salt used to form the arylzinc species from aryl bromides is then re‐used to perform the cross coupling of this resulting arylzinc with N‐benzoyl glutarimides at room temperature. The main advantages of the reaction presented are its robustness and ease of use. Indeed, the reactions of organozinc formation and Negishi‐type coupling are performed without precautions toward water or oxygen.magnified image

Stereochemical assignment of four diastereoisomers of a maculalactone derivative by computational NMR calculations

Naturally occurring γ-butyrolactones and their synthetic analogues display a wide range of bioactivities. Here, the multicomponent reaction of dimethyl 2-benzyl-3-methylenesuccinate with bromobenzene and benzaldehyde catalyzed by cobalt (II) bromide afforded a maculalactone derivative with three stereogenic centers. This reaction presented moderate diastereoselectivity and yielded different proportions of all the four possible diastereoisomers. The anti:anti (majority), anti:syn, syn:anti, and syn:syn diastereoisomers were isolated and characterized by 1D and 2D NMR experiments. Because the stereochemical assignment of all the diastereoisomers by Nuclear Overhauser Effect Difference (NOEDiff) experiments was not definitive, the 1H and 13C NMR chemical shifts were predicted by theoretical calculations with the density functional theory at the B3LYP/6-31G(d) level. The relative configurations of all the four diastereoisomers were assigned by using the CP3 parameter to compare the experimental and the calculated data and by determining the CP3 probability, which provided high level of confidence.

Sonochemical synthesis of a new cobalt(II) complex: Crystal structure, thermal behavior, Hirshfeld surface analysis and its usage as precursor for preparation of CoO/Co3O4 nanoparticles

A bidentate Schiff base ligand and its nano-structured cobalt(II) complex were synthesized under ultrasound irradiation and then their structures were identified by physical and spectral techniques SEM and XRD techniques were used to confirm the nanostructure character of the complex. Single crystal X-ray diffraction analysis showed that the complex crystallizes in the triclinic system with space group of P1¯ and two crystallographically independent molecules participate in its asymmetric unit. In the structure of complex, cobalt center is four-coordinated by two iminic nitrogens of bidentate Schiff base ligand and two bromide anions in a distorted tetrahedral geometry. Crystal packing analysis well indicates that C–H⋯Br, C–H⋯π and π⋯π are the most intermolecular interactions. Moreover Hirshfeld surface analysis and 2D Fingerprint plots were applied for more investigation of intermolecular interactions. In addition, sonochemically prepared cobalt(II) bromide complex was subjected to calcination process under air atmosphere for preparation of cobalt oxide nanoparticles. The XRD pattern confirmed the simultaneous formation of CoO and Co3O4 nanoparticles.

Magnetic behavior of cobalt bromide hydrates including a deuterated form

The magnetic properties of little examined CoBr2•2H2O and new CoBr2•H2O and CoBr2•D2O are studied. Curie-Weiss fits, χM=C/(T-θ), yield θ of −9.9, 9.4 and 10.0 K, respectively, over a 30–80 K linear range for each. Higher temperature data are fit assuming two moderately separated low lying Kramers doublets, with exchange accounted for in a mean-field approximation. Susceptibility maxima appear at 9.5, 15.4 and 15.5 K, with χmax of 0.163, 0.375 and 0.435emu/mol, respectively. Antiferromagnetic ordering is estimated to occur at 9.0, 13.7 and 13.8 K, in the same order. The ratio Tc/Tmax is 0.95, 0.89 and 0.89, respectively, suggesting little low dimensional magnetic character in singly hydrated systems. Data at lower temperatures for the dihydrate are fit with an antiferromagnetic 3D-Ising model. For singly hydrated systems the large size of χmax prevents this; weakened interchain antiferromagnetic interactions yield enhanced susceptibility maxima. Magnetization data exhibit field induced transitions near 13.5kG for the dihydrate, and near 6.5kG for singly hydrated systems with enhanced hysteresis. These transitions are interpreted as metamagnetic in nature.

Cobalt‐Catalyzed C−C Homocoupling

AbstractAn efficient and easy method for C −C homocoupling was developed using cobalt bromide as catalyst. A series of functionalized alkyl bromides and alkyl chlorides were coupled in high yields under mild conditions. This reaction seems to involve a radical intermediate.magnified image

Solubility of d-element salts in organic and aqueous–organic solvents: II. Effect of halocomplex formation on solubility of cobalt bromide and chloride and nickel chloride

Solubility of salts in the systems MCl2–H2O–Solv (M = Co, Ni) and CoBr2–H2O–Solv (Solv = dimethyl sulfoxide, dimethyl formamide, and dimethyl acetamide) at 25°C was measured experimentally. Dominating species of cobalt and nickel halides existing in various concentration regions were identified by analysis of electron absorption spectra. It was shown that the major factor defining solubility is the interaction of halocomplexes of metal ions with solvent molecules.