Phenol, 2- -, cobalt complexes

Of these dyes, Acid Yellow 151 (37) still has the greatest market among the yellows. As reported by USITC, production had increased to 1989 tons in 1985 from 706 tons in 1975. It is produced by coupling diazotized 2-amino-l-phenol-4-sulfonamide to acetoacetanilide followed by metallizing with cobalt to obtain a 1 2 cobalt complex. Acid Orange 24 (38), which is sulfanilic acid coupled to resorcinol to which diazotized mixed xyUdines have been coupled, is an unsymmetrical primary diasazo dye with a bihinctional coupling component. 

Oxidative phenolic coupling.1 This cobalt complex and the related salcomine (2, 160, 3, 245 6, 507), both of which bind oxygen reversibly (102 2Co), catalyze the oxygenation of the phenol 1 to give carpanone 2 in 90-94% yield. Related complexes ol l c(ll) and Mn(II) are less effective. PdCl2 effects this reaction in 46% yield (4, 17(1) singlet oxygen is less efficient (29% yield). 

Figure 9-27. The oxidation of phenol to 1,4-benzoquinone by dioxygen is catalysed by cobalt complex 9.13.

Suitable coupling components are acetoacetanilides for preparing yellow, pyrazolones for red, naphthols for blue and black, naphthylamines for green, and phenols for brown chromium and cobalt complex dyes. A combination of aceto-... 

A cobalt complex salcomine (7.39) oxidizes substituted phenols but unsubstituted at para position, such as 2,6-di-fert-butylphenol (7.40), to give the corresponding p-quinone, 2,6-di- tert-butyl-p-benzoquinone (7.41). 

The proposed reaction mechanism of phenols with O2 catalyzed by Co-amine complexes is shown in Scheme 47. On oxidation of 2,6-dimethylphenol (206) to 2,6-dimethyl-p-benzoquinone (223), magnetic field effects in the cobalt(II)-catalyzed oxidations were examined by using two different high- and low-spin cobalt(II) complexes. The former complex, Co bis(3-(salicylideneamino)propyl)methylamine, Co SMDPT (S = 3/2), displays a maximum increase in the initial rate of ca 1000 G, while the low-spin cobalt complex, Co iV,iV -bis(salicylidene)ethylenediamine, Co salen (S = 1/2), in a 1 10 ratio with pyridine displays a maximum decrease in the initial rate at ca 800 G. The difference in the magnetokinetics of both complexes is explained by magnetic field effects on the singlet-triplet (S-T) radical pair and triplet-triplet (T-T) annihilation reactions... 

Cobalt complexes of vinylketene by reaction with alkynes in the presence of 2 moles of cyclooctadiene 100°C during 20 hours resulted in moderate yields of phenols (ref. 17). This procedure represents the first synthesis of alkylphenols by the insertion of (fi -indenyl)cobalt(l) into a cyclobutenone, the latter being prepared by analogy with a method for cpCo(PPh3)2. With symmetrical alkynes (R = = Et) the yield was 65%, although with unsymmetrical compounds the... 

The reaction of propargyl alcohols with dicobalt octacarbonyl to give the complex salts 148 (X = BF4 or PF6) and synthetic uses of the latter have been reviewed. The salts react with electron-rich aromatic compounds ArH, such as anisole, phenol or N,N-dimethylaniline, to yield substitution products 149 after oxidative demetallation with an iron(III) or cerium(I V) salt with j5-diketones or j -keto esters the corresponding propargyl-substituted compounds 150 are obtained k Acetone reacts in an analogous fashion to give 151. The action of the cobalt complexes 148 on allylsilanes 152 leads to enynes 153. Indole reacts with the complex 148 (R = H R = R = Me) in the presence of boron trifluoride etherate to give 154, which was converted into 155 by the action of iron(III) nitrate " ... 

The cobalt(III)-promoted hydrolysis of amino acid esters and peptides and the application of cobalt(III) complexes to the synthesis of small peptides has been reviewed. The ability of a metal ion to cooperate with various inter- and intramolecular acids and bases and promote amide hydrolysis has been investigated. The cobalt complexes (5-10) were prepared as potential substrates for amide hydrolysis. Phenolic and carboxylic functional groups were placed within the vicinity of cobalt(III) chelated amides, to provide models for zinc-containing peptidases such as carboxypeplidase A. The incorporation of a phenol group as in (5) and (6) enhanced the rate of base hydrolysis of the amide function by a factor of 10 -fold above that due to the metal alone. Intramolecular catalysis by the carboxyl group in the complexes (5) and (8) was not observed. The results are interpreted in terms of a bifunctional mechanism for tetrahedral intermediate breakdown by phenol. 

Decomposition of hydroperoxide 20 in the presence of the cobalt complexes used and Mn(TPP) explains the formation of the quinol 15, and peroxides 29 and 30. During this decomposition, transient free radicals are also formed, which may in turn oxidize the phenol to the phenoxy radical. The role of 20 and its decomposition suggests that adventitious hydroperoxides in certain solvents may in principle also be involved. 

As cobalt complex-mediated oxygenation of these hindered phenols (11) occurs 30 times faster than base-catalyzed oxygenation 62), the phenolato Co(III) complex (12) evidently possesses special activation for reaction with molecular oxygen. In keeping with the desirability of a localized, soft anionic center in an oxygenase substrate, we can only assume that the metal is able to localize the n-anionic charge into an orbital with more [sp ] character. 

These 5-coordinate cobalt complexes form mononuclear superoxo and bridged dinuclear -peioxo complexes, which are reactive toward phenolic substrates, thereby initiating catalytic oxidation cycles ... 

The principle cost determinant in typical hydrolytic or phenolic resolutions is the cobalt catalyst, despite the relatively low catalyst loadings used in most cases and the demonstrated recyclability with key substrates. From this standpoint, recently developed oligomeric (salen)Co complexes, discussed earlier in this chapter in the context of the hydrolytic desymmetrization of meso-epoxides (Scheme 7.16), offer significant advantages for kinetic resolutions of racemic terminal epoxides (Table 7.3) [29-31]. For the hydrolytic and phenolic kinetic resolutions, the oligo-... 

Although coordination of the heterocyclic nitrogen does not occur, two cobalt(II) complexes of 3-hydroxy-5-hydroxymethyl-2-methyl-4-formylpyridine have been isolated with stereochemistry [Co(34-H)A] 2H2O (A = NO3, OAc) [173], For both complexes coordination is ONS (deprotonated phenolic oxygen), but magnetic or electronic spectral data are not included. 

Anionic complexes can easily be prepared by the sulfonation of the aromatic rings in the complexes. Sulfonated cobalt phthalocyanine intercalated in a layered double hydroxide host was a stable catalyst for the oxidation of thiols162,163 and phenol derivatives.164 It was concluded that the complex has been intercalated with the plane of the phthalocyanine ring perpendicular to the sheet of the host (edge-on orientation) (Fig. 7.2). 

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