Nickel -cyclam complex, axial

The electrocatalytic activity of various nickel macrocycles in aqueous solution was studied. Cyclic voltammograms indicate that 7 / S -NiHTIM2+, NiMTC2+ and NiDMC + are better catalysts than Ni(cyclam)2+ in terms of more positive potentials and/or their larger catalytic currents [26], Bulk electrolyses with 0.5 mM Ni complexes confirm that these complexes are excellent catalysts for the selective and efficient CO2 reduction to CO. The macrocycles with equatorial substituents showed increased catalytic activity over those with axial substituents. These structural factors may be important in determining their electrode adsorption and CO2 binding properties. 

There are five basic forms for the trans or planar metal complexes which contain 1,4,8,11-tetraazacyclotetradecane, cyclam, or the hexamethyl analog, CTH. These forms arise due to the combinations of the configurations of the four asymmetric coordinated secondary amine nitrogens present in these systems. Each secondary amine proton is approximately in an axial position and either resides above or below the plane containing the nickel and four nitrogen atoms. Three of these forms are nonenantiomeric (I, II, and III, Fig. 1) and two are enantiomeric (IV and V, Fig. 1). The numerals 3 and 2 in Fig. 1 represent the three and two carbon chains, respectively, which span adjacent coordinated secondary amines. The + and — notation represents secondary amine protons above and below the plane,... 

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