Metal tetraazamacrocyclics

King, G., S.J. Higgins, and N. Price (1992). Novel conducting polymers incorporating covalently bound metal-tetraazamacrocycle complexes. Analyst 117, 1243-1246. 

Higgins, S.J., T.J. Pounds, and PA. Christensen (2001). Synthesis and electro (co)polymerization of novel thiophene- and 2,2 5, 2"-terthiophene-functionalized metal-tetraazamacrocycle complexes, and electrochemical and spectroelectrochemi-cal characterization of the resulting polythiophenes. J. Mater Chem. 11, 2253-2261. 

Aliphatic tetraazamacrocycles are well known to be effective in stabilizing Ni in higher oxidation states due to the very strong in plane -interactions which raise the energy of the (metallic) antibonding orbital from which the electron is extracted on oxidation. Table 1 lists characteristics... 

Bradley et al.109 have combined a p-Si photocathode and homogeneous catalysts (tetraazamacrocyclic metal complexes, which had been shown to be effective catalysts for C02 reduction at an Hg electrode110) to reduce the applied cathode potential. The catalysts showed111 reversible cyclic voltammetric responses in acetonitrile at illuminated p-Si electrodes at potentials significantly more positive (ca. 0.4 V) than those required at a Pt electrode, where the p-Si used had surface states in high density and Fermi level pinning112 occurred. Electrolysis of a C02-saturated solution (acetonitrile-H20-LiC104 1 1 0.1 M) in the presence of 180 mM... 

Tetraazamacrocyclic complexes131 of cobalt and nickel were found110 to be effective in facilitating the reduction of C02 at -1.3 to -1.6 V versus SCE (Table 8). An acetonitrile-water mixture and water were used as solvents, while in dry dimethylsulfoxide no catalytic reduction of C02 took place. Using an Hg electrode, both CO and H2 were produced, where total current efficiencies were greater than 90%. The turnover numbers of the catalysts were 2-9 h 1. The catalytic activity lasted for more than 24 h and the turnover numbers of the catalysts exceeded 100. A protic source was required to produce both CO and H2, and the authors suggested that both products may arise from a common intermediate, which is most likely a metal hydride. The applied potential for C02 reduction was further reduced by using illuminated p- Si in the presence of the above catalysts.111... 

CONTENTS Preface. George W. Gokel. Cryptophanes Receptors for Tetrahedral Molecules, Andre Collett, Jean-Pierre Dutasta and Benedict Lozach. Inclusion Polymerization in Steroidal Canal Complexes, Kiichi Takemoto, Mikiji Miyata. Functionalized Tetraazamacrocycles Ligands with Many Aspects, Thomas A. Kaden. Calixarenes as the Third Supramolecular Host, Seiji Shinkai, Kyushu University, Japan. Fluorescent Chemosensors for Metal and Non-Metal Ions in Aqueous Solutions Based on the Chief Paradigm, Anthony W. Czamik. Index. 

In comparison with some other metal ions, limited synthetic work has been carried out on chromium(III) complexes with macrocyclic ligands. The vast majority of reported complexes involve tetraazamacrocycles. 

Hence, in this work, we report the heterogeneization of this new chiral macrocycle onto micelle-templated silicate (MTS) surface by substitution of chlorine atom of previously grafted 3-chloropropyl chain. After A-alkylation of the tetraazamacrocycle with propylene oxide and metalation with Mn(lI)Cl2, the catalytic performance of the corresponding hybrid materials was evaluated in the heterogeneous enantioselective olefin epoxidation. 

An area of increasing interest is the selective complexation of Sn2+ and more particularly Pb2+ for the treatment of heavy metal poisoning. Molecular mechanics has been extensively applied to the problem of metal ion selectivity (see Chapter 8) but there have been few studies of lead or tin complexes. The fit of Sn2+ to 18-crown-6 has been considered12811, as has the size selectivity of tetraazamacrocycles with respect to Pb2+ binding131. The binding of Pb2+ to porphyrin-1 has been modeled, though in this case the point of interest was the structural deformations caused by the metal cation11901. 

Figure 6-32. The condensation of 2,6-diacetylpyridine with the diamine in the presence of nickel(n) or other first-row transition metal dications leads to complexes of the tetraazamacrocycle 6.33.

Figure 10-2. Although they are relatively rare in biology, organometallic compounds with metal-carbon bonds are important. An typical example is coenzyme B12. The cobalt is co-ordinated to a tetraazamacrocyclic ligand, and has one axial nitrogen donor heterocyclic ligand and one axial alkyl group. The figure illustrates only the core of the macrocycle and the axial groups.

Figure 3.27 Binding constants for the large metal ion Pb (II) decrease by over six orders of magnitude as the ring size increases in tetraazamacrocycles as a result of the conversion of 5-membered chelate rings (suitable for large metal ions) into six-membered chelate rings (suitable for small metal ions).

Haines, R.I. Pendant arm tri- and tetraazamacrocycles synthesis, structure and properties of their first-row transition metal complexes, Rev. Inorg. Chem. 21 (2001), 165-205. 

Handel, H., Muller, F. R., and Guglielmetti, R. (1983) Lipophilic tetraazamacrocycles application to liquid-liquid extraction of metal ions,Helv. Chim. Acta, 66(2), 514-521. 

A number of 14-membered tetraazamacrocyclic complexes serve as catalysts for photochemical and electrochemical CO2 reduction. [CoHMD(H20)](C104)2 (HMD = 5,7,7, 12,14,14-hexamethyl-l,4,8,1 l-tetraaza-cyclotetradeca-4,11-diene) [ 1,2] and Ni(cyclam)Cl2 (cyclam = 1,4,8,11-tetraazacyclotetradecane) [3] have been used as electrocatalysts for the reduction of CO2 in H2O or aqueous CH3CN. The ratio for CO/H2 production is 1 for [CoHMD(H20)](C104)2 and >100 for Ni(cyclam)Cl2. Metal(I) complexes, metal(III) hydride complexes, and metallocarboxylates such as [Ni (cyclam)(C02 )] are postulated as intermediates in the electro- and photo-chemical CO2 reduction [4]. 

Complexes of metals with tetraazamacrocycles possessing pendant arms are currently being considered as models for biologically relevant systems. Such species generally possess a metal ion bound to... 

Alkali metals used to reduce the Co(II) are essential as ions to give CO2 binding to Cod). A large number of Co-7 HC)-C02 complexes have been prepared by this method. The kinetics and equilibrium of CO2 binding to a series of tetraazamacrocycle Cod) complexes,... 

Such hydrido intermediates have been detected in the reactions of Cr2 +, 120,121 Cu +, 122 Fe2 +,123 and Ti3 +.124 The rates of formation of the hydrido species conform to the usual reaction patterns for Id substitution kinetics. An example of H-atom addition to metal complexes is provided by the reaction of [Ni(cyclam)]2 + and a Co (II) tetraazamacrocycle.82,125... 

The C02 radical usually reacts as a simple outer-sphere reductant, but there are examples where it adds to metal centers, reducing them in an inner-sphere mechanism. Two such examples are the reactions with [Ni(cyclam)]2+ and a Co(II) tetraazamacrocycle.82,125... 

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