Zinc-macrocycle complex

Compounds 139 are tris(oximehydrazone) derivatives with an iron(ll) ion in the center of the cavity [230]. Compound 140 (Fig. 38) has been known for 30 years [231, 232] and was prepared from a tris(2-aldoximo-6-pyridyl)phos-phine that is capped by a BF unit to encapsulate cobalt(ll), zinc(ll), nickel(ll), and iron(II). All four macrocyclic complexes were characterized later by a comparative X-ray crystallographic study [233-236]. 

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. 

Complexation and determination of formation constants has been studied with the tetramethyl-cyclam (l,4,8,ll-tetramethyl-l,4,8,ll-tetraazacyclotetradecane) ligand.686 A series of zinc N4 donor macrocyclic complexes with different ring sizes were synthesized and characterized for comparison with cadmium derivatives.687... 

The zinc iodide complex of a 15-membered diamine diimine macrocycle has been structurally... 

The zinc(II) complexes of meso-tetraphenyltetrabenzoporphyrin (38) and of meso-tetraphenyl-tetranaphthoporphyrin (39) have been prepared 173-175 some photophysical properties of this interesting series are given in Table 11176 Photooxidation of zinc(II) porphyrins causes cleavage of the macrocycle with formation of bilinone derivatives.122 206 207... 

The use of a lipophilic zinc(II) macrocycle complex, 1-hexadecyl-1,4,7,10-tetraazacyclododecane, to catalyze hydrolysis of lipophilic esters, both phosphate and carboxy (425), links this Section to the previous Section. Here, and in studies of the catalysis of hydrolysis of 4-nitrophenyl acetate by the Zn2+ and Co2+ complexes of tris(4,5-di-n-propyl-2 -imidazolyl)phosphine (426) and of a phosphate triester, a phos-phonate diester, and O-isopropyl methylfluorophosphonate (Sarin) by [Cu(A(A(A/,-trimethyl-A/,-tetradecylethylenediamine)l (427), various micellar effects have been brought into play. Catalysis of carboxylic ester hydrolysis is more effectively catalyzed by A"-methylimidazole-functionalized gold nanoparticles than by micellar catalysis (428). Other reports on mechanisms of metal-assisted carboxy ester hydrolyses deal with copper(II) (429), zinc(II) (430,431), and palladium(II) (432). 

A zinc(II) complex 22a with an alcohol-pendent polyamine has been synthesized (23). The alcoholic OH deprotonates with pifa of 8.6 (determined by pH-metric titration), yielding 22b. Reaction of 22 (2 mM) with a phosphotriester diethyl(4-nitrophenyl) phosphate (0.1 mM) in 10 mM TAPS buffer (pH 8.6) at 25°C seemed to promote phosphoryl-transfer reactions to 23, just like acyltransferred intermediates 10 and 16a in the reactions between Znn-macrocyclic complexes with an alcohol pendent and NA (see Scheme 4). The pH dependence of the first-order rate constants gave a sigmoidal curve with an inflection point around the pKa value of 8.6. The hydrolysis of the substrate phosphotriester to the phosphodiester product diethyl phosphate thus seemed to... 

The transamination of open-chain ligands may be used in the preparation of macrocyclic complexes, and the template condensation of the zinc complex of 2,6-diacetylpyridine... 

P-Amino imine complexes can also be synthesized from template reactions of p-amino ketones and amines. This approach has been applied to the amino ketone (45), which can be formed by acidic hydrolysis of a zinc(II) macrocyclic complex (Scheme 9).94-95... 

Kimura, E., Koike, T., Shionoya, M., Shiro, M., A versatile macrocyclic [12]aneN3 for interconversion of tetrahedral and trigonal bipyramidal zinc(II) complexes - relevance to 4-coordinate <- 5-coordinate geometries of zinc(II) in carbonic-anhydrase. Chemistry Letters 1992, 787-790. 

IV.A. A Long Alkyl-Pendant Macrocyclic Tetraamine and Its Zinc(ll) Complex... 

Kimura, E. and Kikuta, E. (2000) Macrocyclic zinc(II) complexes for selective recognition of nucleobases in single- and double- stranded polynucleotides, Prog. React. Kinetics Mech. 25, 1-64... 

Although strictly not a dendritic system, Agar et al.[75] have reported the preparation of copper(n) phthalocyaninate substituted with eight 12-membered tetraaza macrocycles as well as its nickel(n), copper(n), cobalt(n), and zinc(n) complexes. Thus, the use of the l,4,7-tritosyl-l,4,7,10-tetraazacyclododecane offers a novel approach to the 1 — 3 branching pattern and a locus for metal ion encapsulation. 

The only other example of a Schiff base condensation with dipyridine to form a macrocyclic complex has been reported by Tasker et al.112) in which 2,6-diformyl-pyridine or 2,6-diacetylpyridine is condensed with 6,6 -dihydrazmo-2,2 -dipyridine (132) in the presence of zinc(II) to afford a pentagonal bipyramidal complex 133. The rigidity of the system results in an equatorial Ns donor set that is essentially planar water molecules occupy the axial positions. 

Many dithiocarbamate complexes of zinc, silver, cadmium or mercury improve emulsion stability, including bis(dibenzyldithiocarbamato)-zinc(II) or -cadmium(II) and silver(I) diethyldi-thiocarbamate. Cadmium salts, mixed with citric acid or tartaric acid and added to the emulsion, are reported to be effective. Mercury(II) complexes of ethylenediaminetetraacetic acid (EDTA) and related ligands and of solubilized thiols such as (4) can be used. Other coordination compounds reported include EDTA and related ligand complexes of Co and Mn, mixtures of Co salts with penicillamine (5) and macrocyclic complexes of Ag such as (6). The latter compounds may be used in diffusion transfer systems in which transferred maximum densities are stabilized. 

Complexes of nickel(II), copper(II), cobalt(III), zinc(II), iron(II), palladium(II), plati-num(II) and vanadyl can be obtained. Although the reaction sequence is fairly general for metal ions, it is not easily extendable to substituted 2-aminobenzaldehydes. However, 2-amino-5-me-thylbenzaldehyde has recently been used successfully in the macrocyclization reaction. Although the macrocyclic complexes (67) are very stable to hydrolysis they are susceptible to attack by nucleophiles, as exemplified in equation (25). " The nickel(II) and copper(II) complexes (67) undergo hydrogenation at relatively low pressures. 

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