Cobalt, 9:6 complex with

Concentration limits of the diphosphate-ion, admissible to determination of magnesium and cobalt, manganese and cobalt, zinc and cobalt by spectrophotometric method with application of the l-(2-pyridylazo)-resorcinol (PAR) are presented. Exceeding maintenance of the diphosphate-ion higher admissible supposes a preliminary its separation on the anionite in the H+-form. The optimum conditions of cobalt determination and amount of the PAR, necessary for its full fastening are established on foundation of dependence of optical density of the cobalt complex with PAR from concentration Co + and pH (buffer solutions citrate-ammoniac and acetate-ammoniac). 

The cobalt complex is usually formed in a hot acetate-acetic acid medium. After the formation of the cobalt colour, hydrochloric acid or nitric acid is added to decompose the complexes of most of the other heavy metals present. Iron, copper, cerium(IV), chromium(III and VI), nickel, vanadyl vanadium, and copper interfere when present in appreciable quantities. Excess of the reagent minimises the interference of iron(II) iron(III) can be removed by diethyl ether extraction from a hydrochloric acid solution. Most of the interferences can be eliminated by treatment with potassium bromate, followed by the addition of an alkali fluoride. Cobalt may also be isolated by dithizone extraction from a basic medium after copper has been removed (if necessary) from acidic solution. An alumina column may also be used to adsorb the cobalt nitroso-R-chelate anion in the presence of perchloric acid, the other elements are eluted with warm 1M nitric acid, and finally the cobalt complex with 1M sulphuric acid, and the absorbance measured at 500 nm. 

It is noteworthy that, as early as 1929, Shibata and Tsuchida reported a kinetic resolution of rac-3,4-dihydroxyphenylalanine by selective oxidation of one enantiomer using a chiral cobalt complex [Co(en)3NH3Cl]Br2 as a catalyst [46,47]. Figure 12 shows a highly enantioselective addition of diisopropy-Izinc to 2-(ferf-butylethynyl)pyrimidine-5-carbaldehyde via an autocatalytic process in the presence of a chiral octahedral cobalt complex with ethylenedi-... 

Polarographic studies are reported on thioesters, mainly of the type (140) and (141), and on trichloroethylphosphonites. In the field of nucleotides and nucleosides it is found that ATP has a very high surface activity at the mercury electrode, which is strongly dependent upon complex formation with transition metals. The polarographic behaviour of cobalt complexes with triphenylphosphine and its oxide has been studied in order to estimate extraction efficiencies. 

The intermolecular Pauson-Khand reaction of the resulting S/P-cobalt complexes with norbornadiene was studied under thermal and A -oxide activation conditions. Thus, heating the diastereomerically pure complex (R = Ph, R = Cy) with ten equivalents of norbornadiene at 50 °C in toluene afforded the corresponding exo-cyclopentenone in a quantitative yield and with an enantio-selectivity of 99% ee. Under similar conditions, the analogous trimethylsilyl complex (R = TMS, R = Cy) afforded the expected product in a high yield but with a lower enantioselectivity of 57% ee. In order to increase this enantio-selectivity, these authors performed this reaction at room temperature in dichloromethane as the solvent and in the presence of NMO, which allowed an enantioselectivity of 97% ee to be reached. These authors assumed that the thermal activation promoted the isomerisation of the S/P ligand leading to a nonstereoselective process. 

Cobalt Complexation with 2-ethyl-amino-5-nitrosophenol, extraction with dichloroethane Spectrophotometry at 402 nm < 0.07 jxg/1 [224]... 

Cobalt Complexation with 4-(2-thiazolylazo) resorcinol, adsorption on XAD-4, resin elution with methanohchloroform Graphite furnace AAS - [234]... 

More recently, Coates et al. reported well-defined cobalt complexes with high catalytic activity and regioselectivity [25-27]. The key concept for the... 

A ligand which links the cobalt complexes with those of chromium and iron is the scorpiand diammac in its isomeric trans and cis conformations (see Scheme 5). 

Up to now, the solubility decrease of cobalt complexes with these modiflers has not been explained satisfyingly. It is assumed that the changes in the solvatization characteristics observed are caused by different interactions of the solute with the mixture of organic components and CO2 the modifier-solute (olefin/aldehyde-complex) interaction probably is stronger than the solute-scC02 interaction. Future theoretical treatment may also improve the... 

Cobalt complexes with square planar tetradentate ligands, including salen, cor-rin, and porphyrin types, all catalyse the reduction of alkyl bromides and iodides. Most preparative and mechanistic work with these reactions has used cobalamines, including vitamin-B,. A generalised catalytic cycle is depicted in Scheme 4.10 [219]. At potentials around -0.9 V vs. see, the parent ligated Co(lll) compound un-... 

The final product is ferrocyanide and cobaltic EDTA, but this goes through an intermediate which can be isolated, and which is an adduct of these twro. Dr. Wilkins tried this system out in his rapid flow rate system and found a rate of association which was about right for substitution rates on a cobaltous ion. So this seemed to be a case where perhaps the nitrogen end of a cyanide was able to coordinate into a cobaltous complex, with either concomitant cr subsequent charge transfer. Yet no transfer of ligand occurs in the overall reaction. 

The valency of the complex radicle is the same as that of the central metallic atom when the complex contains only ammonia, substituted ammonia, water, or other neutral group. For example, cobalt in eobaltie. salts is trivalent, and the cobalt complex with ammonia, Co(NI13)8 ", is likewise trivalent copper in cupric sulphate is divalent, and the copper complex, [Cu(NH3)4] , is also divalent. In the same wn.y [Co(NH3)5.H30] " and [Co(NII3)4.(II20)2] " are trivalent, as also [Co(NH3)2.en2]" and [Co.en3] ", where en represents cthyleucdiamine, CH NH2... 

The fluorescence properties of two fulvic acids, one derived from the soil and the other from river water, were studied. The maximum emission intensity occurred at 445-450 nm upon excitation at 350 nm, and the intensity varied with pH, reaching a maximum at pH 5.0 and decreasing rapidly as the pH dropped below 4. Neither oxygen nor electrolyte concentration affected the fluorescence of the fulvic acid derived from the soil. Complexes of fulvic acid with copper, lead, cobalt, nickel and manganese were examined and it was found that bound copper II ions quench fulvic acid fluorescence. Ion-selective electrode potentiometry was used to demonstrate the close relationship between fluorescence quenching and fulvic acid complexation of cupric ions. It is suggested that fluorescence and ion-selective electrode analysis may not be measuring the same complexation phenomenon in the cases of nickel and cobalt complexes with fulvic acid. 

Disubstituted-l,2,4-thiadiphospholes can be prepared by the reaction of thiophosphinato manganese or cobalt complexes with the kinetically stabilized phosphaalkynes <1996JOM(524)67, 1996CHEC-II(4)771>. In a specific example, 3,5-di(l-adamantyl)-l,2,4-thiadiphosphole 127 was prepared by the reaction of the (7]2-thiophosphinito)manganese... 

Pyridine ligands 186 are monodentate, forming complexes of the kind presented by 189. Pyridine is coordinated in the same way in copper acetate 194 [314] and iron rhodanide complexes [315], adducts of cobalt complex with fe(salicylidene)ethyle-nediamine 195 [316] and nickel chelate, formed by tridentate N,S-donor azomethine ligand 196 [317] ... 

Dreos R, Siega P (2006) Kinetics and mechanism of metallacyclization in a chloromethyl-cobalt complex with a salen-type ligand. Organomet 25 5180-5183... 

But the champion is vitamin B12, a complicated cobalt complex with a three-dimensional structure of great intricacy. No chemist would learn this structure but would look it up in an advanced textbook of organic chemistry. You will find it in such books in the index under vitamin B12 and not under its systematic name. We do not even know what its systematic name might be and we are not very interested. 

Only two reports deal with the reactions of cobalt complexes with HFA. Insertion into the cobalt-hydrogen bond of a hydride complex affords a cobalt hexafluoroisopropylate 136a). An oxolene(2) is formed from an alkylcobalt compound and HFA 66). For mechanistic reasons the authors favor the depicted structure 157 over the isomeric oxolene (3) ring reported for the analogous iron complex 149 174). 

Reduction by nucleoi ilic attack of the original metal hydride has been own to occur under stoichiometric reaction conditions, for instance in the reduction of acyl cobalt complexes with CoH(CO) . Kinetic considerations, Imwever, make it unlikely that such a sequence plays a major role in the hydroformylaiion process. In fact, the rate-determining step, corresponding to the hydrogenolysis of the acyl complex, is slowed by an increase of carbon... 

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