Cobalt complexes purine

Involvement of two nucleophilic nitrogen atoms is thus typical for the amino heterocycles. The mutual disposition of the pyridine and amine nitrogen atoms allows the formation of chelate structures for the cobalt complexes of purine, 221 and 222. Structures with the N, iV -five-membered metal cycles were proven for the tri- and tetranuclear complexes of silver ) with 8-aminoquinoline (223) (92IC4370), and polymeric copper- and rhodium-acetate clusters (224). Another coordination mode can be found in the complexes of 4-amino-3,5-bis(pyridin-2-yl)-l,2,4-triazole, (225 or... 

For unsubstituted purines, the most probable site for coordination is the imidazole nitrogen (N-9), which is protonated in the free neutral ligand. An example is the cobalt complex of adenine, [Co(ad)2(H20)4]+ (9-XXII). 

The rate constants for the reaction of [Ni(nta)(H20)a] with various ligands in their neutral and protonated forms have been reported, as has that for the formation of the bis-complex of nickel(n) with the purine base theophylline. Rate constants have also been reported for the formation of bis-complexes of cobalt(n), nickel(n), and copper(n) with L-proline, L-hydroxypyroline, glycyl-L-leucine, , L-Ieucylglycine, a-alanine, jS-alanine, iminodiacetic acid, iminodipropionic acid, and aspartic acid. ... 

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