Polyaza-macrocycles, metal complexes

Macrocyclic complexes of zinc have inspired interest in varied areas such as supramolecular and biomimetic chemistry including hydrolysis enzymes, such as phosphatases and esterases, and also for the fluorescent detection of zinc. The polyaza macrocycles and their A--functionalized derivatives are particularly well represented. An important aspect of macrocycle synthesis is the use of metal templates to form the ligand. Examples of zinc as a template ion will be discussed where relevant. 

The protonated polyaza macrocycles (27-6H+ and 28-8H+) also complex metal hexacyanide anions (81CC1067). Both Fe(CN)64- and Ru(CN)64- form 1 1 complexes which are more difficult to oxidize than the uncomplexed anion. The shifts in anodic oxidation potential are independent of the M(CN)64- species involved but vary with the size of the macrocycle (+130 mV for 27-6H+ and +165 mV for 28-8H+). This suggests that the redox potential of complexed anions is controlled by electrostatic effects due to the charge of the surrounding macrocycle. 

Virtually all types of metal ions have been complexed with macrocyclic ligands.2-7 Complexes of transition metal ions have been studied extensively with tetraaza macrocycles (Chapter 21.2). Porphyrin and porphyrin-related complexes are of course notoriously present in biological systems and have been receiving considerable investigative attention (Chapter 22).8 Macrocyclic ligands derived from the Schiffbase and template-assisted condensation reactions of Curtis and Busch also figure prominantly with transition metal ions.6,7 The chemistry of these ions has been more recently expanded into the realm of polyaza, polynucleating and polycyclic systems.9 Transition metal complexes with thioether and phosphorus donor macrocycles are also known.2... 

Thioether analogs of the crowns have been known since the 1930s,103 but metal ion complexes of these ligands have not been investigated with the intensity found for the crowns and polyaza macrocycles. As anticipated from the soft nature of the heteroatom, the sulfur macrocycles show a preference to bind transition metals rather than alkali and alkaline earth ions. Studies have... 

Numerous stability constants for metal complexes with triaza-, tetraaza-, and polyaza-macrocycles have been measured. Smaller rings, with three and four nitrogen atoms, generally form 1 1 species ML (but sometimes also ML2). Larger rings with more nitrogen donors can give protonated species MLHn and/or binuclear complexes M2L. 

Polyaza macrocycles like 15 are of interest due to their capability of forming complexes with transition metals [28] and anions, e.g. carboxylates [29], phosphates [30] and even ATP [31]. 

An extensive review of the thermodynamic aspects of polyaza macrocycles has been reported. Other reviews include the chemistry of tridentate and pentadentate aza macrocycles, 1,4,7-triazacyclononane and derivatives, and polyaza macrocycles with pendant chains. In general, the polyaza macrocycles form extremely stable complexes with transition metals of the later transition series, bnt show rednced affinity for alkali and alkaline earth metal ions compared to the oxa macrocycles. 

Polyaza macrocycles with pendant arms have been stndied extensively, in particular with respect to protonation and complexation as well as to the kinetics of metal complex formation. These aspects are treated in a review by Kaden. Of particular interest is the fact that metal complex formation constants of macrocycles with pendant carboxylates can be 10 to 10 times higher than for the unsubstituted analogs. 

Transition metal complexes of the larger polyaza macrocyclic ligands have been less extensively studied than for the smaller ring systems. For the pentaaza macrocycles, [ISJaneNs with ethylene bridges appears to form the most stable complexes with most metal ions. Structural data for a variety of pentaaza macrocyclic complexes have been reviewed. The N-H bonds as well as the different sized chelate rings must be considered in calculating the... 

The hexaaza [ISJaneNe forms complexes with transition metal ions and with certain alkali and alkaline earth and lanthanide ions. For the higher aza macrocycles with seven or more donor atoms, dinuclear complexes become possible. A systematic investigation of both the structural and thermodynamic aspects of copper complexes formed with the larger polyaza macrocycles from heptaaza to dodecaaza has been published. All of the macrocycles were found to form hydroxo species as well as polynuclear complexes. A number of structures have been determined for the higher polyaza macrocycles, both in complexed and noncomplexed forms, and structures range from highly boat shaped to nearly planar. ... 

The metal-templated cyclocondensation of the appropriate dicarbonyl precursor with a functionalized diamine gives the so-called bibracchial (doubly pendant-armed) SB macrocycles (Scheme 20). This area has been reviewed.20 Pendant arm macrocycles and their metal complexes have also attracted attention. Arms bearing additional potential ligating groups have been introduced at both carbon and nitrogen atoms of macrocycles which have generally been based on polyaza or... 

Reaction of selected metal ion complexes of multidentate amines with formaldehyde and a variety of activated carbon compounds (such as nitro-methane or diethyl malonate) have led to ring closure to yield polyaza macrocycles (Comba et al., 1986 Lawrance and O Leary, 1987). Reaction with the malonate ester gave less than a 2% yield. Another approach for the... 

Metal complexes of polyaza and polyoxaaza Schiff base macrocycles 05CCR(249)2156. 

Polyaza-, polythia-ligands. Recognition of transition metal ions. Replacing the oxygen sites with nitrogen or sulphur yields macrocycles and cryptands that show marked preference for transition metal ions and may also allow highly selective complexation of toxic heavy metals such as cadmium, lead and mercury [2.41-2.44, A.14]. 

The pure polyphospha macrocycles (12) (as opposed to the mixed donor phospha macrocycles) were first reported in 1975. These macrocycles have been found to complex a variety of transition metals, but have not received the same attention as the more readily accessible polyaza and polyoxa macrocycles. 

Ogden, M. Spencer, P. New polyaza and polyammonium 33. ferrocene macrocyclic ligands that complex and electro-chemically recognize transition metal cations and phosphate anions in water. Chem. Commun. 1993, 13, 1046. 

M. Shakir, K. S. Islam, A. K. Mohamed, M. Shagufta, and S. S. Hasan, Macrocyclic complexes of transition metals with divalent polyaza units, Transition Metal Chemistry, vol. 24, no. 5, pp. 577—580, 1999. 

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