Cyclam macrocycle

Reaction of [Ni(TMTAA)] with acid in the presence of A1C13 gives complex (606) that features two isolated diimine units in the six-membered chelate rings (Equation (21)),1535 while hydrogenation of [Ni(TMTAA)] leads to fully saturated cyclam macrocycles (607) (Equation (22)) 1536... 

A nontrivial synthetic approach to multinuclear cyanide-bridged clusters was developed by Comba and co-workers (208), who used ligand XXII capable of encapsulating up to three Cu(II) ions inside the cyclam macrocycles connected to the central triazine ring. In this case, the very nature of the building block promotes the formation of high nuclearity complexes. Indeed, when the [Cu°3(XXII)] ... 

There is potentiometric evidence for the formation of a mercury(III) complex by the oxidation of the mercury(II) complex of the cyclam macrocycle 1,4,8,11-tetraazacyclotetradecane. There is also some evidence for the biological oxidation of mercury to Hg . 

The family of bis(cyclam macrocycles) represented by 32, in which the cyclam subunits are linked through nitrogen atoms by — (CH2) — (n = 2-4), m-xylyl, or p-xylyl groups, has been synthesized (58). The di-Ni(II) and di-Cu(II) complexes of these bis(macrocycles) have been used in an investigation of the effects of mutual electrostatic interaction on the redox behavior of the respective metal centers. 

A similar structure based on a cyclam macrocycle (two opposite bridges between the four nitrogen atoms are one carbon longer) is also commonly encountered. The presence of the carboxylic moieties ensures the high stability. 

With a tridentate ligand Au(terpy)Cl3.H20 has, in fact, AuCl(terpy)2"1" with weakly coordinated chloride and water while Au(terpy)Br(CN)2 has square pyramidal gold(III) the terpyridyl ligand is bidentate, occupying the axial and one basal position [124]. Macrocyclic complexes include the porphyrin complex Au(TPP)Cl (section 4.12.5) cyclam-type macrocyclic ligands have a very high affinity for gold(III) [125],... 

Countless macrocycles containing basic functionalities have been synthesized and, for a large number of compounds, values have been determined (Patai, 1980 Gokel and Korzenowski, 1982 Kaden, 1984 Kimura, 1985 Lindoy, 1989 Vogtle, 1989, 1991 Gokel, 1991, 1992 Izatt et al., 1991, 1992 Dietrich et al., 1993). Usually, the basic function in these macrocycles is a nitrogen atom the compounds are (poly)azamacrocycles. But in azacrowns like [1] or cyclams [2] the /n-orientation of the lone pair at the nitrogen atom is not assured. Murakami et al. (1991) synthesized the... 

B = a tetraamido macrocycle, cyclam-acetate = l,4,8,ll-tetramethyl-l,4,8,ll-tetraaza-cyclo-... 

Stability of Complexes of the Porphyrin TSPP Compared with the Nitrogen Donor Macrocycles Cyclam and THEC, with Metal Ions of Biological Interest"... 

The 14-membered macrocycle 1,4,8,11-tetraazacyclotetradecane (cyclam or [14]aneN4), unlike cyclen, is capable of encircling most transition metal ions and in the case of Co111 the trans configuration is much preferred by comparison with the folded cis isomer. Electrochemical reduction of A,v-[Co(cyclam)(OI I)2]+ in 3M NaOH leads to rapid isomerization to the trans form, and the relative stabilities of the trans and cis isomers of the di- and trivalent complexes were determined from a thermodynamic cycle.702 This preference for trans orientation of the non-macrocyclic donors has enabled the isolation and investigation of many Co complexes without the complications of isomerization. Some novel examples include /r[Pg.61]

With respect to the ring size, it has been stated that neither the redox potentials nor the half-lives of the Ni species are directly correlated to the cavity of the macrocyclic ligand, but the redox potentials are dependent on solvation effects.139 The effect of fused benzene rings and ring conformation has been monitored.140 In Ni complexes of fluorine-containing cyclams (25) the higher oxidation state becomes successively destabilized with respect to Ni, while the lower oxidation state (i.e., Ni1) becomes successively stabilized.141... 

In a comparative study, the semiempirical PM3(tm) method was shown to be less effective than molecular mechanics for modeling the structures of Ni11 complexes with tetraaza macrocycles.398 In contrast, local DFT calculations (VWN5 method), coupled with appropriately large basis sets, accurately describes the geometries of the isomers of [Ni(cyclam]2+. 

Enantiomerically pure cyclam-type ligands derived from L-proline have been prepared via multistep procedures and shown to form complexes of Ni11, e.g., (593).1508 The Ni11 ion in (594) is encapsulated by a face-to-face bis(macrocyclic) ligand that forms upon treatment of [Ni(tren)2]2+ with formaldehyde.1509... 

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