Mechanistic and kinetic studies of cobalt macrocycles in a photochemical CO{sub 2} reduction system. Evidence of CO-CO{sub 2} adducts as intermediates
- Brookhaven National Lab., Upton, NY (United States)
- Osaka Univ. (Japan)
Cobalt macrocycles mediate electron transfer in the photoreduction of CO{sub 2} with p-terphenyl as a photosensitizer and a tertiary amine as a sacrificial electron donor in a 5:1 acetonitrile/methanol mixture. The mechanism and kinetics of this system have been studied by continuous and flash photolysis techniques. Transient spectra provide evidence for the sequential formation of the p-terphenyl radical anion, the Co{sup 1}L{sup +} complex, the [Co{sup 1}L-CO{sub 2}]+ complex, and the [S-Co{sup 111}L-(Co{sub 2}{sup 2-})]{sup +} complex (L = HMD = 5,7,7,12,14,14-hexamethyl-1,4,8,11-tetraazacyclotetradeca-4, 11-diene; S = solvent) in the catalytic system. The electron-transfer rate constant for the reaction of p-terphenyl radical anion with Co{sup II}L{sup 2-} is 1.1 x 10{sup 10} M{sup -1} s{sup -1} and probably diffusion controlled because of the large driving force (approximately + 1.1 V). Flash photolysis studies yield a rate constant 1.7 x 10{sup 8} M{sup -1} s{sup -1} and an equilibrium constant 1.1 x 10{sup 4} M{sup -1} for the binding of CO{sub 2} and Co{sup 1}L{sup +} in the catalytic system. These are consistent with those previously obtained by conventional methods in acetonitrile. 60 refs., 8 figs., 2 tabs.
- Research Organization:
- Brookhaven National Lab. (BNL), Upton, NY (United States)
- DOE Contract Number:
- AC02-76CH00016
- OSTI ID:
- 81316
- Journal Information:
- Journal of the American Chemical Society, Vol. 117, Issue 25; Other Information: PBD: 28 Jun 1995
- Country of Publication:
- United States
- Language:
- English
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