Cobalt complexes applications

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). 

Another application of salen ligands is the hydrolytic kinetic resolution of epoxides (Scheme 3). For this purpose cobalt complexes are efficient, and fiu-... 

INDUSTRIAL AND ANALYTICAL APPLICATIONS OF COBALT COMPLEXES 6.1.4.1 Organic Transformations... 

Alkali metal boratabenzenes have a wide synthetic applicability just like alkali metal cyclopentadienides. Two syntheses have been developed Ashe s synthesis via organotin intermediates (23) and our cyanide degradation of bis (boratabenzene) cobalt complexes (61). 

As an example of the application of this method we can consider the cobalt complexes of bis(salicyldeneamine-3-propyl)amine,... 

If a chiral cobalt complex, instead of Co(salen)2, is used, enantioselectivity during the ring-opening process is induced (at —20°C the optimal ee was 76%) <2002CC28>. The application of stabilized Horner-Wadsworth-Emmons phosphonates represents a viable alternative to ylides in the cyclopropanation reaction <2002JOC3142>. 

The application of perfluorous polyethers in biphasic catalysis was first described by Vogt (133), who also synthesized ligands based on hexafluor-opropene oxide oligomers to create metal complexes that are soluble in the perfluorous polyethers. The solvophobic properties of the fluorous solvent were successfully incorporated in the metal complexes catalytic oligomerization and polymerization reactions with nickel and cobalt complexes were demonstrated. 

Chromium and cobalt are the metals most commonly used in dyestuffs for polyamide fibres and leather because of their kinetic inertness and the stability of their complexes towards acid. Since the advent of fibre-reactive dyestuffs, chromium and cobalt complexes have also found application as dyestuffs for cellulosic fibres, particularly as black shades of high light-fastness. Copper complexes are of more importance as dyes for cellulosic fibres and are unsuitable for polyamide fibres because of their rather low stability towards acid treatments. 

There is no doubt that Schetty s rules have a certain validity but great care must be exercised in their application since structural features of azo compounds other than their coordinating system can dramatically affect the geometry of the derived 1 2 chromium and cobalt complexes. 

It must be concluded, therefore, that the ligands do not become completely detached from the metal ion in isomerization reactions. Comparable results have been observed in the isomerization95 of potassium diaquodioxalatochromium(III) and the racemization96 of optically active potassium tris(oxalato)chromium(III) when no exchange with free ligand in solution occurs. Thus, although it is not practicable to take advantage of the desirable properties of individual isomers of 2 1 chromium and cobalt complexes of tridentate azo compounds because of the facility with which such compounds isomerize in solution, the technically important unsymmetrical 2 1 complexes are capable of practical application because they show little or no tendency to disproportionate in solution. 

Cobalt complexes find various applications as additives for polymers. Thus cobalt phthalocyanine acts as a smoke retardant for styrene polymers,31 and the same effect in poly(vinyl chloride) is achieved with Co(acac)2, Co(acac)3, Co203 and CoC03.5 Co(acac)2 in presence of triphenyl phosphite or tri(4-methyl-6- f-butylphenyl) phosphite has been found to act as an antioxidant for polyenes.29 Both cobalt acetate and cobalt naphthenate stabilize polyesters against degradation,73 and the cobalt complex of the benzoic acid derivative (12) (see Section 66.4) acts as an antioxidant for butadiene polymers.46 Stabilization of poly(vinyl chloride)-polybutadiene rubber blends against UV light is provided by cobalt dicyclohexyldithiophosphinate (19).74 Here again, the precise structure does not appear to be known. 

Finally, several complexes of chiral /J-thioxoketones have been prepared510 and the cobalt complex 149 has found an interesting synthetic application as catalyst in asymmetric cyclopropanation reactions (equation 157)511. 

Indoline, in trinuclear Ru and Os clusters, 6, 725 Indolizidine, via cyclization-hydrosilylation, 11, 389-390 Industrial processes, in Ziegler-Natta polymerizations, 4,1040 Inflammation, drugs for, 12, 460 Infrared spectroscopy applications, 1, 501 cobalt complexes, 1, 488... 

Alkynes too have found application in the synthesis of oxepanes. The A/B ring system (45) of ciguatoxin has been formed in a stereoselective manner by cyclisation of the alkyne cobalt complex (44) with boron trifluoride followed by reductive removal of the chromium with... 

Nature demonstrates that transition metals can be very effective in catalyzing transformations, which are impossible to accomplish otherwise under physiological conditions. The prime example is vitamin B12, whose resting state is adenosylco-balamine(III) (reviews [267-273]). On homolysis it triggers a variety of radical reactions crucial to the living world. This inspired the interest of chemists and led to a number of applications. More recently, interest shifted to catalysis by low-valent cobalt complexes. 

Acid dyes include metal-complexed azo structures, where the metals used are cobalt, chromium, and iron.10 Examples are 1 1 and 2 3 chromium complexes and 1 2 cobalt complexes, where the numbers employed represent the ratio of metal atoms to dye molecules. Metal-complexed dyes can be formed inside textile fibers by treating suitably dyed fibers with a solution containing metal ions.11 In this case, the metal-free forms of these azo dyes are known as mordant dyes and contain mainly ortho, ortho -bis-hydroxy or ortho-carboxy, ortho -hydroxy groups (e.g., C.I. Mordant Black 11, Mordant Yellow 8, and Mordant Orange 6). When the metal complexes are formed prior to the dye application process, the resultant dyes are known as... 

Most catalytic systems used in industrial production yield polyalkenes with very long chains which are unsuitable for current processing procedures and applications. For regulating molecular mass, H2 is preferred to organometal-lics. Hydrogen is not a suitable transfer agent in diene polymerizations on cobalt complexes [67] because it reduces the Co (II) zr-allylic centre to inactive Co (I) particles. 

A mechanism (Equation (2S)) has been suggested from stoichiometric studies on cobalt complexes, but it seems (o be of limited application. 

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