Published April 25, 1990 | public
Journal Article

Effects of redox potential, steric configuration, solvent, and alkali metal cations on the binding of carbon dioxide to cobalt(I) and nickel(I) macrocycles

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Abstract

The binding of CO₂ to metal macrocycles has been determined electrochemically by using cyclic voltammetry or differential pulse polarography. The CO₂ binding constants, K_(CO₂), 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,l stereoisomers of [Coᴵ(Me₆[14]4,l 1-diene)]⁺ had identical redox potentials, K_(CO₂) 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 K_(CO₂) and the solvent dielectric constant was found for d,l-[Co(Me₆[14]4,11-diene)]⁺. In tetrahydrofuran (THF), d,l-[Co(Me₆[14]4,11-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 K_(CO₂)'s for Co(salen)⁻ and Co(Me₂salen)⁻ in THF indicated a strong dependence on redox potential and electrolyte cation.

Additional Information

© 1990 American Chemical Society. Received September 14, 1989. We gratefully acknowledge J. Endicott for forwarding a preprint of ref 29 and thank E. Fujita and C. Creutz of Brookhaven National Laboratories for numerous helpful discussions concerning unpublished research on similar systems. We thank B. Balazs for a sample of Ni(cyclam)(ClO_4)_2. This research was funded by the Gas Research Institute. N.S.L. also acknowledges support as a Dreyfus Teacher-Scholar and from the NSF Presidential Young Investigator Program.

Additional details

Created:
August 19, 2023
Modified:
October 18, 2023