1,4,7,10-Tetraazacy clododecanes

Neutral N-derivatized octadentate ligands based on cyclen (1,4,7,10-tetraazacy-clododecane) form tripositive cationic complexes with the trivalent lanthanides [116-124]. The N-substituted tetraamide derivatives have proven useful in understanding the relationship between the solution structure of the Ln3+ complex and its water exchange rate, a critical issue in attaining optimal relaxation efficiency of CA s [125-131]. 

Lanthanide complexes with macrocyclic ligands such as those based on 1,4,7,10-tetraazacy-clododecane or polyaminocarboxylates have been studied extensively by CPL spectroscopy. These complexes often possess large stability constants in aqueous solution and, moreover, present interesting chiroptical properties. There have been a number of reports of CPL... 

Several pieces of evidence suggest the operation of this E2 mechanism for base hydrolysis of the d5-[Co(cyclen)Cl2] cation (cyclen = 1,4,7,10-tetraazacy-clododecane, 34, In the first place, the large difference in rate constant between this complex and its bromo analog is too large to be explained convincingly on the basis of an 5n1C5 mechanism, but perfectly acceptable if the E2 mechanism operates. Secondly, a comparison of the kinetic parameters k,, and... 

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