Cyclam nickel derivatives

Table 6.1 summarizes the thermodynamic parameters relating to the macrocyclic effect for the high-spin Ni(n) complexes of four tetraaza-macrocyclic ligands and their open-chain analogues (the open-chain derivative which yields the most stable nickel complex was used in each case) (Micheloni, Paoletti Sabatini, 1983). Clearly, the enthalpy and entropy terms make substantially different contributions to complex stability along the series. Thus, the small macrocyclic effect which occurs for the first complex results from a favourable entropy term which overrides an unfavourable enthalpy term. Similar trends are apparent for the next two systems but, for these, entropy terms are larger and a more pronounced macrocyclic effect is evident. For the fourth (cyclam) system, the considerable macrocyclic effect is a reflection of both a favourable entropy term and a favourable enthalpy term. 

Ni(II) complexes of cyclam and oxocyclam derivatives catalyze the epoxidation of cyclohexene and various aryl-substituted alkenes with PhIO and NaOCl as oxidants, respectively. In the epoxidation catalyzed by the Ni(II) cyclam complex using PhIO as a terminal oxidant, the high-valent nickel- complexes (e.g., LNiin-0, LNi=0, LNiin-0-... 

Dong, Y., Lawrance, G. A., Lindoy, L. F., and Turner, P. (2003) Macrocyclic ligand design. Interaction of a series of successively N-benzylated derivatives of 1,4,8,11-tetraazacyclotetradecane (cyclam) with copper(II) and nickel(II), Dalton Trans. (8), 1567-1576. 

The tetradentate ligand, 1,4,8,11-tetraazacyclotetradecane (cyclam), forms solid diamagnetic orange to brown Ni(II) complexes with iodide and perchlorate anions (9). When the anions are changed to chloride and bromide, the solid complexes are paramagnetic (9). However, all the complexes are soluble in water, methanol, and benzene, giving yellow solutions. The yellow color remains on treatment with 12N HCl and excess chloride ion (9). It is interesting to note that this amine is a derivative of a reduction product of the template syntheses between bis(ethylenediamine)-nickel(II) and acetone reported earlier. 

Derivatives of [14]N4(10) (cyclam) even in low doses have a good efficiency in reducing the lethal response to nickel. These macrocycles significantly enhance the urinary and biliary excretion of Nr and restore the altered levels of other trace metal ions such as Cu-+, Zn-, and Fe They are more efficient in this application than linear chelating agents such as EDTA or triethylenetetraamine (Athar et al., 1987 Misra et al., 1988). 

Ni(II) complexes of cyclam and oxocyclam derivatives catalyze the epoxidation of cyclohexene and various aryl-substituted alkenes with PhIO and NaOCl as oxidants, respectively. In the epoxidation catalyzed by the Ni(II) cyclam complex using PhIO as a terminal oxidant, the high-valent nickel-oxo complexes (e.g., LNi -0, LNi=0, LNi -0-I-Ph, or LNi -0-Ni L) have been proposed as the active oxidant (92). In the reaction, E olefins are more reactive than the corresponding Z isomers, and a strong correlation was observed between the electron-donating effect of the para substituents in styrene and the initial reaction rate (91). Isotope labeling studies have shown that the epoxide oxygen is derived from PhIO. 

Rotating-copper-disk electrode techniques have been used to evaluate the efficiency of the nickel macrocycle catalyst for the reduction of CO2 to Studies have been performed using Ni(diazacyclam) + (diazacyclam = 3,10-dimethyl-1,3,5,8,10,12-hexaazacyclophane) (5.6), a complex derived from cy-clam, which appears to be more active than [Ni(cyclam)2] " under the same conditions (see Figure 5.70) . These results are consistent with a mechanism proposed by other authors - . ... 

Tetraheterodecalin podands, their linkers, and resulting macrocycles A hoard of constitutionally and stereochemically dynamic systems 13IJC45. Thermodynamics and kinetics of CO2, CO, and H binding to the metal centre of CO2 reduction catalysts, in particular, cobalt and nickel complexes of 1,4,8,11-tetraazacyclotetradecane (cyclam) and its derivatives 12CSR2036. 

A monomeric molecule of a nickel (Il)-cyclam derivative covalently linked to pyrrole has been synthesized, resulting in an adhesive conducting film on glassy carbon which presents a reversible behaviour of the Ni(III)/Ni(II) couple [190]. 

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