A Simple and Convenient One-Pot Synthesis of Benzimidazole Derivatives Using Cobalt(II) Chloride Hexahydrate as Catalyst

A simple and efficient method for the convenient synthesis of 2-arylbenzimidazole has been described on reaction with o-phenylenediamine and various aromatic aldehydes using cobalt(II) chloride hexahydrate as a catalyst. The method is cost-effective, high-yielding, clean, and selective.     

Zinc(II) perchlorate hexahydrate catalyzed opening of epoxide ring by amines: applications to synthesis of (RS)/(R)-propranolols and (RS)/(R)/(S)-naftopidils

Commercially available zinc(II) perchlorate hexahydrate [Zn(ClO4)2.6H2O] was found to be a new and highly efficient catalyst for opening of epoxide rings by amines affording 2-amino alcohols in high yields under solvent-free conditions and with excellent chemo-, regio-, and stereoselectivities. For unsymmetrical epoxides, the regioselectivity was influenced by the electronic and steric factors associated with the epoxides and the amines. A complementarity in the regioselectivity was observed during the reaction of styrene oxide with aromatic and aliphatic amines: aromatic amines provided amino alcohols from nucleophilic attack at the benzylic carbon as major products whereas aliphatic amines resulted in formation of the amino alcohols through reaction at the terminal carbon atom of the epoxide ring as the major/sole products. Reaction of aniline with various glycidic ethers gave the amino alcohols by regioselective nucleophilic attack at the terminal carbon atom of the epoxide ring as the only/major product. Zinc(II) perchlorate hexahydrate was found to be the best catalyst compared to other metal perchlorates. The counteranion modulated the catalytic property of the various Zn(II) compounds that followed the order Zn(ClO4)2.(6)H2O>Zn(BF4)2 approximately Zn(OTf)2>ZnI2>ZnBr2>ZnCl2>Zn(OAc)2>Zn(CO3)2 in parallelism with the acidic strength of the corresponding protic acids (except for TfOH). The applicability of the methodology was demonstrated by the synthesis of cardiovascular drugs propranolol and naftopidil as racemates and optically active enantiomers.     

CoCl_2·6H_2O or LaCl_3·7H_2O Catalyzed Biginelli Reaction. One-Pot Synthesis of 3,4-Dihydropyrimidin-2(1 H)-ones

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Efficient Ce(NO3)3 x 6H2O-catalyzed solvent-free synthesis of 3,4-dihydropyrimidin-2(1H)-ones

Cerium(III) nitrate hexahydrate efficiently catalyzes the three-component Biginelli reaction under solvent-free conditions of an aldehyde, a beta-keto ester or beta-diketone and urea or thiourea to afford the corresponding 3,4-dihydropyrimidin-2(1H)-ones or -thiones in excellent yields.     

Efficient Synthesis of 5‐Carboxanilide‐Dihydropyrimidinones Using Cobalt(II) Nitrate Hexahydrate

5‐Carboxanilide‐dihydropyrimidinone derivatives were synthesized in good yield in a three‐component and efficient process by the condensation reaction of acetoacetanilide, aldehyde and urea/thiourea in the presence of cobalt(II) nitrate hexahydrate as catalyst in ethanol at ambient condition.     

Monomeric complexes of 1,8- bis (isonicotinyloxy)anthracene-9,10-dione

Condensation of two equivalents of isonicotinic acid with 1,8-dihydroxyanthraquinone forms 1,8-bis(isonicotinyloxy)anthracene-9,10-dione (1), a potential bridging diester ligand. Complexation reactions between 1 and Co(II) and Ni(II) perchlorate hexahydrate salts produce 2 : 1 ligand : metal monomeric complexes. One nicotinic nitrogen is bonded to a metal center while the second ‘free’ isonicotinic nitrogen is hydrogen bonded to water molecules, present from the hydrated salts used in the synthesis, ligated to the same metal center.     

Improvement of ion chromatography with ultraviolet photometric detection and comparison with conductivity detection for the determination of serum cations

Studies were made of the analytical conditions required for indirect photometric ion chromatography using ultraviolet photometric detection (UV method) for the determination of serum cations following a previously developed serum pre-treatment. The sensitivities of the conductivity detection (CD) and UV methods and the amounts of serum cations determined by both methods were compared. Attempts to improve the sensitivity of the conventional UV method are reported. It was found that the mobile phase previously reported by Small and Miller showed no quantitative response when more than 4 mM copper(II) sulphate pentahydrate was used. As a result, there was no significant difference in the amounts of serum cations shown by the CD and UV methods. However, by adding 0.5-5 mM cobalt(II) sulphate heptahydrate, nickel(II) sulphate hexahydrate, zinc(II) sulphate heptahydrate or cobalt(II) diammonium sulphate hexahydrate to 0.5-1.5 mM copper(II) sulphate pentahydrate, higher sensitivity and a quantitative response were attained.     

Heterotopic helicand for designing heterometallic helicates

A new diazine tetratopic helicand, H4L, is obtained from 3-formylsalicylic acid and hydrazine. The reaction between H4L and cobalt(II) perchlorate, iron(III) perchlorate, and sodium carbonate leads to triple-stranded tetranuclear anionic helicates, [L3Co(II)2Fe(III)2]2-, which are connected through Na ions, resulting in chiral coordination polymers, [L3Na2Fe2Co2(H2O)4(EtOH)2].3H2O.     

Zinc perchlorate catalyzed one-pot synthesis of 3,4-dihydropyrimidinones under solvent-free conditions

Abstract

In this paper, we report zinc perchlorate hexahydrate [Zn(ClO₄)₂?6H₂O] as a highly effective catalyst for the synthesis of 3,4-dihydropyrimidin-2(1H)-ones under solvent-free conditions. These improved reaction conditions allow the preparation of a wide variety of substituted dihydropyrimidinones in high yields and purity under mild reaction conditions. Compared with the classical Biginelli reaction, this method has the advantage of excellent yields and short reaction time in solvent-free conditions.     

A linear S-bridged trinuclear cobalt(III) complex with 2-aminobenzenethiol: synthesis,crystal structure,and spectroscopic characterization

Treatment of cobalt(II) perchlorate hexahydrate with 2?M equiv. of 2-aminobenzenethiol (Habt) in acetonitrile afforded a tricationic tricobalt complex, [Co{Co(abt)₃}₂](ClO₄)₃·2CH₃CN, by aerial oxidation. The molecular structure of the meso (ΔΛ) form of the complex was determined by X-ray crystallography. In the complex cation, the central Co is coordinated by six thiolate groups from two terminal fac(S)-[Co(abt)₃] units in an octahedral geometry, forming a linear S-bridged tricobalt structure.     

Structure and magnetic properties of 2,4,6,8-tetra(<Emphasis Type="Italic">tert</Emphasis>-butyl)phenoxazin-1-one adducts with cobalt(II) salts

Complex formation reaction of redox-active 2,4,6,8-tetra(tert-butyl)phenoxazin-1-one with cobalt(II) chloride leading to the dimeric adduct has been studied. UV spectroscopy studies have revealed the equilibrium of the formed adduct with dissociated form of the complex in the acetonitrile solution. In the presence of ethylene glycol, the complex formation with cobalt(II) perchlorate has afforded the high-spin trimolecular adduct. Crystal structure of the obtained adducts has been studied by means of X-ray diffraction analysis.     

High-energy complex copper(II) perchlorate with 1,5-pentamethylenetetrasole as ligand

Possibility of obtaining an energy-saturated metal complex, copper tetrakis[cyclopentamethylenetetrasol] perchlorate, was studied by reacting copper(II) perchlorate hexahydrate with cyclopentamethylenetetrazol. The composition and structure of the complex were confirmed by elemental analysis and UV, IR, ¹H NMR, and ESR spectroscopies. The thermal decomposition of the metal complex synthesized was analyzed and its explosive characteristics and combustion law, as well as the combustion law of a model formulation of a composite solid propellant with addition of the complex, were determined.     

A new method for enol lactone synthesis by a Michael addition/cyclization sequence

Reactions of cyclic 1,3-dicarbonyl compounds with 1-(2-alkenoyl)-4-bromo-3,5-dimethylpyrazoles under the double catalytic activation conditions using both catalytic amounts of Lewis acid and amine catalysts provide a new direct synthetic route to enol lactones. Thus, 1,3-cyclohexanedione is allowed to react with 4-bromo-1-crotonoyl-3,5-dimethylpyrazole, in tetrahydrofuran at room temperature in the presence of both catalytic amounts (10 mol% each) of nickel(II) perchlorate hexahydrate and 2,2,6,6-tetramethylpiperidine, to give 4,7,7-trimethyl-3,4,5,6,7,8-hexahydrobenzopyran-2(H),5-dione in a good yield. This reaction does not proceed or is too slow under the reaction conditions other than the double catalytic activation conditions.     

Electrochemical studies of azido(imidazole) cobaloxime complexes

Summary Cyclic voltammetric studies of a series of azido(imidazole) cobaloxime complexes in acetonitrile with tetraethylammonium perchlorate as the supporting electrolyte reveal the presence of the central cobalt atom in these complexes in the +III state. In addition to reductions to cobalt(II), cobalt(I) and cobalt(0) species, evidence for oxidation to cobalt(IV) also was noted.     

PREPARATION AND CHARACTERIZATION OF COBALT(III) COMPLEXES WITH SARCOSINE AND SOME TETRADENTATE LIGANDS OF THE EDDA TYPE

Abstract

Meridional geometrical isomers of cobalt(III) complexes with sarcosine (N-methylglycine) and tetradentate ligands edda (ethylenediamine-N,N′-diacetate ion), eddp (ethylenediamine-N,N′-di-3-propionate ion) and 1,3-pdda (1,3-propylenediamine-N,N′-diacetate ion) have been prepared. The edda and eddp cobalt(III) complexes were made by the reaction of sarcosine and sodium ethylenediamine-N,N′-diacetato(carbonato)cobaltate(III), and sodium uns-cis-(ethylenediamine-N,N′-di-3-propionato)(carbonato)cobaltate(III) dihydrate, respectively. The previously synthesized pdda-cobalt(III) complex with sarcosine was obtained by a new route by direct synthesis of cobalt(II) chloride hexahydrate with sarcosine and 1,3-pdda in the presents of lead(IV) oxide. Complexes were isolated chromatographically and characterized by elemental analysis, electron absorption spectra, infrared spectra and ¹H NMR spectroscopy.     

4-Amino-3-pentadecyl-3H-1,2,4-triazole-3-thiones and 3-pentadecyl-1,3,4-oxadiazole-2(3H)-thione for the preparation of dimeric palladium(II) complexes and their applications in Tsuji–Trost and Mizoroki–Heck reactions

The synthesis of palladium complexes derived from 4-amino-3-pentadecyl-3H-1,2,4-triazole-3-thiones and 3-pentadecyl-1,3,4-oxadiazole-2(3H)-thiones are reported. They were obtained from palladium acetate and dipotassium tetrachloropalladate(II) and their composition was assigned by elemental analysis (solid state). The resulting metallic entities were also characterized in solution based in mass spectrometry experiments. Their application in organic synthesis as cross-coupling reaction catalysts is described. One example of both conventional Tsuji–Trost and Mizoroki–Heck reactions were efficiently carried out in very high chemical yield.     

Complexes formed in the chloroform extraction of cobalt(II) with oxine

Absorption spectra of cobalt-oxine complexes-extractedinto chloroform indicate that two cobalt(II) and one cobalt(III) complexes can be extracted depending on pH and the initial concentrations of oxine in the organic phase or cobalt(II) ion in the aqueous phase. The oxidation state of cobalt in the complexes was determined by treatment of organic extracts with an 0.001 M EDTA solution at pH 4–5; cobalt(II) complexes were back-extracted, and the cobalt(III) complex was not. The equilibrium distribution ratios of cobalt(II) between aqueous perchlorate solutions and oxine solutions in chloroform were determined at 20°. A plot of logD_co-log[HO_x]_o vs. pOx gave a single curve for different concentrations of oxine; it was concluded that cobalt(II) is extracted as C_oOx₂HOx.     

Synthesis,spectroscopy, electrochemistry,and methylation reaction of the dithiolate-based cobalt(II) complex derived from tert-butyl N-(2-mercaptoethyl)carbamate

A dithiolate-containing a carbamate mononuclear cobalt(II) complex namely, [Co(Boc-S)₂] (1), was obtained by the reaction of a methanolic solution of cobalt(II) nitrate hexahydrate with two equimolar amounts of the deprotonated form of tert-butyl N-(2-mercaptoethyl)carbamate (Boc-SH). The cobalt(II) complex (1) was characterized in the solid state and in solution by using FT–IR, Raman, UV–visible, and EI–mass spectroscopies, as well as thermal and X-ray diffraction studies. Spectral data showed that the carbamate (Boc-SH) acts as a mono-anionic bidentate ligand coordinating the cobalt(II) ion through two imine nitrogen and two deprotonated thiolate sulfur donor atoms in a distorted tetrahedral geometry. The thermoanalytical data evidence that the complex is stable up to 165 °C and undergoes complete decomposition, resulting in CoO. TEM imaging of the oxide residue shows its nano size clusters, suggesting that the complex (1) may be used as a precursor for nano-oxides. X-ray powder diffraction patterns evidence an isomorphism among the complex. The redox behavior of the cobalt(II) complex was also investigated by cyclic voltammetry. The reaction of the dithiolate cobalt(II) complex (1) with methyl iodide appears to occur intramolecularly with the cobalt-bound dithiolate, forming the cobalt(II)-bound dithioether complex [Co(Boc–SCH₃)₂]I₂ (2), as a dication complex with a clean second-order reaction of 13.24 × 10⁻² M⁻¹·s⁻¹.     

Reaction of Cobalt(III) Diaquatetrammine Cation with 5-(3-Nitrophenyl)tetrazole

A series of cobalt(III) tetrazolate tetrammine complexes were prepared by reaction of cobalt(III) diaquatetraammine perchlorate with 5-(3-nitrophenyl)tetrazole. The factors affecting this reaction were studied. The reaction was thermally activated both by common heating with an external heater and microwave heating. Thermolysis of the tetrazolate complexes was studied.     

Novel copper(II) induced formation of a porphyrinogen derivative: X-ray structural,spectroscopic, and electrochemical studies of porphyrinogen complexes of Cu(II) and Co(III) complex of a trispyrazolyl tripodal ligand

Copper(II) complexes of a novel pyrazole containing porphyrinogen and cobalt(III) and zinc(II) complexes of a pyrazole containing tripodal ligand having N-donor atoms have been investigated. 5-Methyl-3-formylpyrazole (MPA) on reaction with copper(II) nitrate or perchlorate in the presence of tris(2-aminoethyl)amine (tren) forms novel pyrazole-based porphyrinogen complexes [Cu(T(3)-porphyrinogen)(H(2)O)](NO(3))(2) (1a) and [Cu(T(3)-porphyrinogen)(H(2)O)](ClO(4))(2) (1b) where T(3)-porphyrinogen is 1,6,11,16-tetraaza-5,10,15,20-tetrahydroxy-2,7,12,17-tetramethylporphyrinogen. The same products are also obtained when tren is replaced by triethylamine. By contrast, the reaction between MPA, tren, and cobalt(II) perchlorate produces the cobalt(III) complex [Co(HMPz(3)tren)]ClO(4) (2) derived from the tripodal Schiff base tris[4-(3-(5-methyl-pyrazolyl)-3-aza-3-butenyl]amine (H(3)MPz(3)tren). The X-ray crystal structures of the copper(II) complexes (1a and 1b) and the cobalt(III) complex (2) have been determined. The structures show distorted square pyramidal coordination environments for 1a and 1b with the water molecule occupying the apical site, while for complex 2 a distorted octahedral geometry is obtained. Data for 1a follow: a = 19.476(3) A, b = 9.4116(8) A, c = 14.204(3) A; alpha = 90 degrees = gamma, beta = 107.58(2) degrees; V = 2482.0(7) A(3), Z = 4. Data for 1b follow: a = 20.967(3) A, b = 9.1563(18) A, c = 14.858(4) A; alpha = 90 degrees = gamma, beta = 108.44(3) degrees; V = 2706.0(10) A(3), Z = 4. Data for 2 follow: a = 21.293(3) A, b = 12.724(2) A, c = 19.777(4) A; alpha = 90 degrees = gamma, beta = 93.03(2) degrees; V = 5350.6(15) A(3), Z = 8. All three complexes crystallize in the monoclinic crystal system with the C2/c space group. The complexes are further characterized by UV-vis, IR, EPR, and electrochemical studies.