Tetraazamacrocyclic complexes

Ni2+ was very popular in the early days of the investigation of mechanisms of complex formation, since the time-scale for its reactions with simple ligands was so convenient for the then recently developed stopped-flow technique. However, interest has now moved on to other first-row cations, especially to Cu2+. A review of the kinetics and mechanisms of formation of tetraazamacrocyclic complexes concentrates on Ni2+ and Cu2+, and their reactions with cyclam and similar ligands (267). The tetra(4 -sulfonatophenyl)porphyrin complexes of Ni2+ and of Cu2+ react immeasurably slowly with cyanide, but their IV-methyl derivatives do react, albeit extremely slowly. The relevant time scales are hours for removal of Ni2+, months for the removal of Cu2+, by 10-4 M cyanide at pH 7.4 (268). 

It is noted that the (tetragonally distorted) octahedral Ni(II)-tetraazamacrocycle complexes of general formula trans[NiN4X2] are high spin (d8-dvz2dx-2dxi2d 1 dx2 y21). 

Many 14-membered tetraazamacrocyclic complexes of cobalt and nickel serve as catalysts for electrochemical CO2 reduction to produce CO and H2 in water, acetonitrile-water or organic solvents [8-11]. The structures of the macrocycles are shown in Figure 2. Among these, Ni(cyclam) + is a very effective and selective catalyst for the electrochemical reduction of CO2 to CO [10, 11]. Ni(cyclam)+ ad-... 

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]. 

Tetraazamacrocyclic complexes of Ni(II) (Nitrogen is needed) Combined Ce(III), Ce(IV) and Ferroin... 

SCHEME 6.19 Tetraazamacrocyclic complexes for catalytic electrochemical and photochemical reduction of carbon dioxide. 

Similar reactivity towards activated methyl compounds, especially methyl iodide, has been observed for Ni OEiBC [114, 115, 61, 116] and for Ni (tmtaa) (where tmtaa is the dianion of 6,8,15,17-tetramethyl-5,14-dihydro-dibenzo [b,i] [1, 4, 8, ll]tetraazacyclotetradecine) [112, 113]. Ni tmtaa), generated in situ by reduction of Nin(tmtaa) and observed by EPR, was proposed as the active catalyst in the reduction by NaBH4 of alkyl halides to alkanes. Recently, a different Ni(I) tetraazamacrocyclic complex, produced by irradiation of the Ni(II) parent compound with 5 MeV electrons, produced small amounts of methane from subsequently added CH3S-CoM [111]. The represented the first report of reactivity of any identifiably Ni(I) species with the natural substrate. 

The tetraazamacrocyclic complex (66) adopts a saddle shape about Ni and allows the formation of a 1 1 supramolecular complex with Ceo and a 2 1 complex with other... 

Synthesis and Characterization of Biologically Active 10-Membered Tetraazamacrocyclic Complexes of Cr(III), Mn(III), and Fe(III)... 

Taraszewska, J., G. Roslonek, and B. Korybut-Daszkiewicz (2000). Redox properties of novel dinuclear Ni(II) bis-tetraazamacrocyclic complex. Supramol. Chem. 12(1), 115-121. 

Rowinski, P. and R. Bilewicz (2001). Carbon dioxide electrochemical sensor based on lipid cubic phase containing tetraazamacrocyclic complexes of Ni(II). Materials Science and Engineering C 18(1-2), 177-183. 

Kashiwagi, Y, C. Kikuchi, F. Kurashima, and J. Anzai (2002). Electrocatalytic reduction of aldehydes and ketones on nickel(II) tetraazamacrocyclic complex-modified graphite felt electrode. J. Organomet. Chem. 662(1-2), 9-13. 

Although the electrochemistry and the electrocatalytic properties of nickel macrocyclic complexes, phthalocyanines and porphyrins have been well studied in various solvents, few data exist on their special and typical behaviour when electropolymerized films in aqueous alkaline solution. During the last decade, it has been shown that nickel tetraazamacrocyclic complexes (examples shown in Figure 8.20) can be easily deposited onto an electrode surface in alkaline solutions... 

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. 

Cobalt macrocychc, or pseudo-macrocyclic, complexes have proven among the most widespread cobalt-based proton reduction catalysts. For example, Fisher and Eisenberg demonstrated in 1980 that some cobalt tetraazamacrocyclic complexes are active in both CO2 and reduction [75]. Similarly, porphyrins have been extensively investigated. Nocera and coworkers showed that cobalt(II) hangman porphyrins can catalyze proton reduction with less overpotential and weaker acids than their standard porphyrin cousins (Fig. 13d) [85, 86]. Both features are thought to be a result of the enhanced proton donation by the carboxylic acid of the hangman substituent. Bren and coworkers showed that the biologically derived cobalt-substituted microperoxidase-11 is stable with a turnover number of 25,000, but the catalytic rate is relatively low at 6.7 s [87]. 

Much more information is available for Co tetraazamacrocyclic complexes. The cobalt(I) corrin systems (compounds modeling vitamin Bj2) have been most thoroughly studied. 

NEW DEVELOPMENTS IN VOLTAMMETRIC BEHAVIOUR AND ELECTROCATALYTIC ACTIVITY OF Nl(ll) TETRAAZAMACROCYCLIC COMPLEXES... 

In our work we were interested to study 1) the electrochemical behaviour of selected Ni-tetraazamacrocyclic complexes with pendant amino group in dependence on the pH of solution, 2) the electrocatalytic activity of these complexes and 3) the influence of solvent on the heterogenous kinetics of Ni(II)/Ni(III) redox couple in these complexes. 

Taraszewska, J., Rosl onek,G., and Korybut-Daszkiewicz,B. (1991) "Voltammetric behaviour of Ni(II) and Co(III) tetraazamacrocyclic complexes containing a pendant amino group", J.Electroanal.Chem., 297, 245-255. 

Roslonek,G, and Taraszewska,J. "Electrocatalytic oxidation of alcohols on glassy carbon electrodes electroche-mically modified with nickel tetraazamacrocyclic complexes. Mechanism of film formation", J.Electroanal.Chem., (in press). 

Taraszewska, J.,and Roslonek,G., "Effect of solvent on the kinetic and thermodynamic redox properties of Ni(III)/ Ni(II) in tetraazamacrocyclic complexes with pendant amino group and cyclam studied on the glassy carbon electrodes", J.Electroanal.Chem.,(in press). 

Template synthesis of other chiral tetraazamacrocyclic complexes can also be achieved [252-254]. The corresponding complexes are obtained according to Scheme 2-16. 

An unusual template reaction is performed in the case of complexes of dioximes and their derivatives reacting with CO2. Starting from malonamide oxime the tetraazamacrocyclic complex [Ni(L1833)] is obtained (Eq. 9.7) [15]. Structures of [Ni(L1833)] (Figure 9-2) and of its quasimacrocyclic precursor [Ni(L1832)] were established by X-ray crystallography [15]. 

Metal porphyrins act as catalysts for chain transmission in radical polymerisation [55] and for electrochemical oxidation of sulphur dioxide [64], as well as for oxidation of a wide range of organic substrates [65]. Cobalt and nickel complexes with LI5 are effective in the electrocatalytic reduction of carbon dioxide [66]. Porphyrin complexes of cobalt and tetraazamacrocyclic complexes of nickel catalyse reduction of the proton [67-71]. 

Villagran M, Muena JP, Ferraudi G, Zagal JH, Costamagna J (2009) Electrochemical reduction of S(IV) species in aqueous medium by glassy carbon electrodes modified with polymeric copper(II) tetraazamacrocyclic complexes. J Coord Chem 62 141-149... 

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