Bidentate aliphatic amines

The use of an extended arene (tetrahydroanthracene) in [OsCl(en)(ri6-tha)]+ (29) gave rise to a similar potency (112). This is in contrast with the data for ruthenium-arenes, where the same substitution gave rise to a 10-fold increase in activity. Further work therefore needs to determine if the extended Os-arenes can intercalate into DNA in a manner similar to Ru-arenes. Replacement of the iV /V-chelating ligand en for other AyV-bidentates with pyridine, aliphatic amine, or azopyridine donor atoms leads to loss of activity, probably because of slower hydrolysis and higher acidity of the coordinated water (112). 

For the latter CNS receptor ligands, different types of chelators have been introduced to the basic receptor binding framework. Originally a bidentate Schiff base was introduced by the reaction of an aliphatic amine with pyridine-aldehyde. Labelling occurred at low concentration and the radio conjugate was physiologically stable. Although receptor affinity was fully retained, brain uptake was low [67]. ACp was introduced at the same position and, as described earlier, and receptor affinity was perfectly retained. No brain uptake data are... 

The synthesis and reactivities of substituted aliphatic bidentate complexes are similar to the reactions of analogous ethylenediamine complexes. Basolo and co-workers prepared619 and studied the rates of chloride aquation555 of a variety of trails-[Rh(N N)2 Cl2 ]+ complexes (NN = meso-bn, where bn = 2,3-diaminobutane (+)-bn, and tetrameen—both cis and trans isomers) the rate of chloride release is not dramatically dependent on the nature of the aliphatic amine ligand. 

Table 1 covers many of the important considerations of the chelate effect in transition metal complexes. It is divided to show examples of two-coordinate, three-coordinate, and fonr-coordinate binding constants. First, examination of the data shows that the chelate effect is not confined to a par-ticnlar metal-ligand system, as seen for Ni + and Cu ", and is operable for both aliphatic and aromatic amines. For simple bidentate ligands such as en and bipy, the chelate effect ranges from 2.27 for Ni(en) + to 3.94 for Ni(bipy) +, and is larger for bipy than en with the same metal ion. 

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