The binding of CO2 to metal macrocycles has been determined electrochemically by using cyclic voltammetry or differential pulse polarography. The CO2 binding constants, KCO2, for a series of Co(I) tetraazamacrocycle complexes in (CH3)2SO showed a strong correlation with the Co(II/I) redox potential. Although meso and d,1 stereoisomers of [CoI(Me64,11-diene)]+ had identical redox potentials, KCO2 differed by a factor of 102 for these stereoisomers, suggesting a large steric effect on CO2 binding. Binding of CO2 to Ni(I) tetraazamacrocycles in (CH3)2SO yielded a redox potential dependence similar to that of Co(I) macrocycles. A weak correlation between KCO2 and the solvent dielectric constant was found for d,l-[Co(Me6-4,11-diene)]+. In tetrahydrofuran (THF), d,l-[Co(Me64,11-diene)]+ was found to bind CO2 more strongly in the presence of 0.1 M Li+ than in the presence of 0.1 M tetrabutylammonium (TBA+). Electrochemically determined KCO2's for Co(salen)- and Co(Me2salen)- in THF indicated a strong dependence on redox potential and electrolyte cation.
|Number of pages||7|
|Journal||Journal of the American Chemical Society|
|Publication status||Published - Apr 25 1990|
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