Cobalt amino complex

These workers also found that the adsorption of Co(ll) was higher on the ammonia-treated samples compared with the C02-activated carbon samples. It has been suggested that in the former case, the adsorption process involves the formation of some cobalt-amino complexes such as [Co(NH3) ] + in which the cobalt is present as Co " ions so that the adsorptive removal of Co(II) is higher. The adsorption of Co(ll) on activated carbons increased considerably in the presence of anions such as CF, Br", CH3COO", NOf, and S20f, and decreased in the presence of tartrate and citrate ions. It was suggested that the former anions were adsorbed on the carbon... 

Introduction of the cobalt atom into the corrin ring is preceeded by conversion of hydrogenobyrinic acid to the diamide (34). The resultant cobalt(II) complex (35) is reduced to the cobalt(I) complex (36) prior to adenosylation to adenosylcobyrinic acid i7,i -diamide (37). Four of the six remaining carboxyhc acids are converted to primary amides (adenosylcobyric acid) (38) and the other amidated with (R)-l-amino-2-propanol to provide adenosylcobinamide (39). Completion of the nucleotide loop involves conversion to the monophosphate followed by reaction with guanosyl triphosphate to give diphosphate (40). Reaction with a-ribazole 5 -phosphate, derived biosyntheticaHy in several steps from riboflavin, and dephosphorylation completes the synthesis. 

Methyl-5-amino-l-formylisoquinoline thiosemicarbazone, 22, also yields cobalt(II) complexes from unheated methanol solution [202]. However, due to this ligand s added steric requirements, a complex, [Co(22)Cl2], with one ligand per metal ion center is formed. This brown solid has a magnetic moment of 4.42 B.M., is a non-electrolyte, has coordination of a neutral NNS ligand, and the electronic spectrum indicates approximate trigonal bipyramidal stereochemistry. 

Fanali, S., Ossicini, L., Foret, F., and Bocek, R, Resolution of optical isomers by capillary zone electrophoresis study of enantiomeric and distereoisomeric cobalt (III) complexes with ethylenediamine and amino acid ligands, /. Microcol. Sep., 1, 190, 1989. 

Macrocyclic Fi-donor ligands and vitamin Bj, analogues. The free amine [(97) tet] can be prepared from the previously reported nickel complex. Cobalt-fin) complexes have been prepared with both planar (bcde octahedral) and folded (abed octahedral) co-ordination. Derivatives of the three ligand configurations arising from restricted inversion at the four chiral co-ordinated secondary amino-groups have been prepared (see Scheme 2) and their stabilities and configurations discussed. ... 

The preparation of oximes from olefins is a valuable approach for the synthesis of nitrogen-containing compounds such as amino acids and heterocycles. Okamoto and colleagues have reported that a catalytic reduction-nitrosation of styrenes 31 with ethyl nitrite and tetrahydroborate anion by the use of bis(dimethylglyoximato)cobalt(II) complex afford the corresponding acetophenone oximes 32 (Scheme 23). 

Schollkopf, U. Enantioselective Synthesis of Nonproteinogenic Amino Acids. 109, 65-84 (1983). Shibata, M. Modern Syntheses of Cobalt(III) Complexes. 110, 1-120 (1983). ... 

Eujii Y, Matsutani K, Kikuchi K. Formation of a specific coordination cavity for a chiral amino-acid by template synthesis of a polymer Schiff-base cobalt(III) complex. Chem Commun 1985 415-417. 

Complexes of other amino acids or their derivatives with cobalt(II) that have been investigated include dipeptides (120) these complexes have long been known to absorb dioxygen. For example, the mononuclear cobalt(II) complex of N, N,N", N "-diglycylethylenediaminete-traacetic acid (121) absorbs one mole of dioxygen per two moles of complex. This system has been proposed as a simple, convenient model system for the study of dioxygen complexes of cobalt(II) peptides in solution because of its relatively slow conversion to the irreversibly formed cobalt(III) dioxygen complex. 

For tridentate amino acids with three non-equivalent donor atoms such as L-aspartic acid or L-cysteine, the isomers possible are illustrated below (252-254). There have been a number of reports of the preparation of L-aspartic acid complexes.1180,1181,1182. In the earlier work the isomers were not identified, however in the later study, the complexes were tentatively identified by comparison of their spectroscopic properties with those of the corresponding cobalt(III) complexes.1183 The order of elution of the complexes on HPLC was also similar to that observed for the corresponding cobalt(III) complexes. Mixed complexes containing l- or D-aspartate and L-histidine were also prepared.1182 A crystal structure of one salt obtained from this kind of system, bis(L-histidinato-0,Ar,Ar )chromium(III) nitrate, has been determined.1184... 

A study74 of cobalt complex formation by a series of related o,o -diaminodiarylazo compounds showed that, in marked contrast to the l-(2-hydroxyphenylazo)-2-naphthylamine (62d), l-(2-aminophenylazo)-2-naphthylamine (63) reacted with cobalt(II) chloride to give a 2 1 cobalt(III) complex (64) in which only one proton had been lost from each ligand molecule. This observation led to the proposal that proton loss occurred from the iminohydrazone form of the ligand rather than from a primary amino group. 

Many more recent stoichiometric studies of cobalt(III) complexes have been responsible for most of the developments in this area of research. Cobalt(III) ammine complexes effect hydrolysis of ethyl glycinate in basic conditions via intramolecular attack of a coordinated amide ion hydrolysis by external hydroxide ion attack also occurs (equation 74).341 Replacement of ammonia ligands by a quadridentate or two bidentate ligands allows the formation of aquo-hydroxo complexes and enables intramolecular hydroxide ion attack on a coordinated amino ester, amino amide... 

Coordinated a-amino amides can be formed by the nucleophilic addition of amines to coordinated a-amino esters (see Chapter 7.4). This reaction forms the basis of attempts to use suitable metal coordination to promote peptide synthesis. Again, studies have been carried out using coordination of several metals and an interesting early example is amide formation on an amino acid imine complex of magnesium (equation 75).355 However, cobalt(III) complexes, because of their high kinetic stability, have received most serious investigation. These studies have been closely associated with those previously described for the hydrolysis of esters, amides and peptides. Whereas hydrolysis is observed when reactions are carried out in water, reactions in dimethyl-formamide or dimethyl sulfoxide result in peptide bond formation. These comparative results are illustrated in Scheme 91.356-358 The key intermediate (126) has also been reacted with dipeptide... 

In the case of inert cobalt(m) complexes it is possible to isolate the chelated products of the reaction. Let us return to the hydrolysis of the complex cations [Co(en)2(H2NCH2C02R)Cl]2+ (3.1), which contain a monodentate iV-bonded amino acid ester, that we encountered in Fig. 3-8. The chelate effect would be expected to favour the conversion of this to the chelated didentate AO-bonded ligand. However, the cobalt(iu) centre is kinetically inert and the chloride ligand is non-labile. When silver(i)... 

In conclusion, the hydrolytic and other reactions of co-ordinated amino acid derivatives with nucleophiles may proceed by two major routes. The first involves a moderate acceleration by general acid catalysis of a monodentate TV-bonded ligand, whilst the second may involve very dramatic rate increases (by a factor of a million or so) associated with didentate chelating TV O-bonded ligands. There is little evidence for the widespread involvement of co-ordinated nucleophiles attacking the carbonyl in amino acid derivatives, although some special, and well characterised, examples with cobalt(m) complexes are considered in the next chapter. 

We saw in Chapter 3 that the hydrolysis of chelated amino acid esters and amides was dramatically accelerated by the nucleophilic attack of external hydroxide ion or water and that cobalt(m) complexes provided an ideal framework for the mechanistic study of these reactions. Some of the earlier studies were concerned with the reactions of the cations [Co(en)2Cl(H2NCH2C02R)]2+, which contained a monodentate amino acid ester. In many respects these proved to be an unfortunate choice in that a number of mechanisms for their hydrolysis may be envisaged. The first involved attack by external hydroxide upon the monodentate A-bonded ester (Fig. 5-62). This process is little accelerated by co-ordination in a monodentate manner. 

A stimulating discussion of the chemistry cobalt(m) complexes of amino acid derivatives... 

Figure 7-9. The condensation of the cobalt(m) complex of the hexadentate ligand 7.4, which contains three primary amino groups, with formaldehyde and ammonia, gives the encapsulated complex 7.5. A view of the cation 7.5 as found in the solid state structure of its perchlorate salt is also presented.

In the synthesis of the symmetrical 1 2 cobalt azomethine complex 19 [41043-60-1] [31], a mixture of 2-amino-6-nitrophenol-4-sulfonic acid and salicylaldehyde is heated to boiling in sodium acetate solution. The suspension is cooled and mixed first with CoCl2-6H20 and then with 30% H202. The resulting solution is salted out with NaCl and KC1. The dye yields exceptionally lightfast yellow colors on wool and polyamides. 

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