Abstract
The thermodynamics and kinetics of binding of CO2, CO, and H+ to N-racemic and N-meso stereoisomers of the cobalt(I) macrocycle CoL+ (L = 5,7,7,12,14,14-hexamethyl-1,4,8,11-tetraazacyclotetradeca-4,11-diene) have been determined in aqueous media with use of the pulse radiolysis technique and transient ultraviolet-visible spectroscopy. N-rac- or N-meso-CoL+ was produced by the hydrated electron reduction of N-rac- or N-meso-CoL2+, with tert-butyl alcohol generally added to scavenge hydroxyl radicals. Reactions of both N-rac- and N-meso CoL+ are readily followed by the disappearance of intense (ε 1 × 104 M-1 cm-1) absorption bands at 630 and 635 nm, respectively. The product absorptions are much less intense (ε 200-500 M-1 cm-1) and shifted to higher energy (400-500 nm). Carbon dioxide adducts were also produced via the reactions of N-rac- or N-meso-CoL2+ with formate radical .CO2 - in solutions containing sodium formate and CO2 and hydrogen ion adducts (hydrides) by the reactions with .H atom in acid solution. The known stereochemistry of the methyl radical additions to N-rac- and N-meso-CoL2+ was used to assign the different isomers of the adducts. Thus, reaction of •H and •CO2+ with N-rac-CoL2+ yields sec-N-rac-CoL(H)2+ and sec-N-rac-CoL(CO2)+, respectively, and the reaction of N-rac-CoL+ with H+ and CO2 yields prim-N-rac-CoL(H)2+ and prim-N-rac-CoL(CO2)+, respectively. As expected, only N-meso adducts are obtained from either N-meso-CoL+ or N-meso-CoL2+. Formation constants for the complexes (determined by analysis of equilibrium absorptions or equilibration kinetics) at 25°C are CoL(CO2)+, 2.5 × 108 M-1 (prim-N-rac), 6.0 × 106 M-1 (N-meso); CoL(CO)+, 1.6 × 108 M-1 (prim-N-rac), 0.8 × 108 M-1 (N-meso); CoL(H)2+, 2.5 × 1011 M-1 (prim-N-rac), ≥7.9 × 1013 M-1 (N-meso). The rate constants are large and generally parallel the stability of the adduct. The following are values of k (M-1 s-1) for addition at 25°C: CO2, 1.7 × 108 (prim-N-rac), 1.5 × 107 (N-meso); CO, 5.0 × 108 (prim-N-rac), 8.3 × 108 (N-meso); H+, 3.0 × 109 (prim-N-rac), 2.3 × 109 (N-meso).
| Original language | English |
|---|---|
| Pages (from-to) | 3361-3371 |
| Number of pages | 11 |
| Journal | Journal of the American Chemical Society |
| Volume | 113 |
| Issue number | 9 |
| Publication status | Published - 1991 |
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Thermodynamics and kinetics of carbon dioxide binding to two stereoisomers of a cobalt(I) macrocycle in aqueous solution. / Creutz, Carol; Schwarz, Harold A.; Wishart, James F.; Fujita, Etsuko; Sutin, Norman.
In: Journal of the American Chemical Society, Vol. 113, No. 9, 1991, p. 3361-3371.Research output: Contribution to journal › Article
}
TY - JOUR
T1 - Thermodynamics and kinetics of carbon dioxide binding to two stereoisomers of a cobalt(I) macrocycle in aqueous solution
AU - Creutz, Carol
AU - Schwarz, Harold A.
AU - Wishart, James F.
AU - Fujita, Etsuko
AU - Sutin, Norman
PY - 1991
Y1 - 1991
N2 - The thermodynamics and kinetics of binding of CO2, CO, and H+ to N-racemic and N-meso stereoisomers of the cobalt(I) macrocycle CoL+ (L = 5,7,7,12,14,14-hexamethyl-1,4,8,11-tetraazacyclotetradeca-4,11-diene) have been determined in aqueous media with use of the pulse radiolysis technique and transient ultraviolet-visible spectroscopy. N-rac- or N-meso-CoL+ was produced by the hydrated electron reduction of N-rac- or N-meso-CoL2+, with tert-butyl alcohol generally added to scavenge hydroxyl radicals. Reactions of both N-rac- and N-meso CoL+ are readily followed by the disappearance of intense (ε 1 × 104 M-1 cm-1) absorption bands at 630 and 635 nm, respectively. The product absorptions are much less intense (ε 200-500 M-1 cm-1) and shifted to higher energy (400-500 nm). Carbon dioxide adducts were also produced via the reactions of N-rac- or N-meso-CoL2+ with formate radical .CO2 - in solutions containing sodium formate and CO2 and hydrogen ion adducts (hydrides) by the reactions with .H atom in acid solution. The known stereochemistry of the methyl radical additions to N-rac- and N-meso-CoL2+ was used to assign the different isomers of the adducts. Thus, reaction of •H and •CO2+ with N-rac-CoL2+ yields sec-N-rac-CoL(H)2+ and sec-N-rac-CoL(CO2)+, respectively, and the reaction of N-rac-CoL+ with H+ and CO2 yields prim-N-rac-CoL(H)2+ and prim-N-rac-CoL(CO2)+, respectively. As expected, only N-meso adducts are obtained from either N-meso-CoL+ or N-meso-CoL2+. Formation constants for the complexes (determined by analysis of equilibrium absorptions or equilibration kinetics) at 25°C are CoL(CO2)+, 2.5 × 108 M-1 (prim-N-rac), 6.0 × 106 M-1 (N-meso); CoL(CO)+, 1.6 × 108 M-1 (prim-N-rac), 0.8 × 108 M-1 (N-meso); CoL(H)2+, 2.5 × 1011 M-1 (prim-N-rac), ≥7.9 × 1013 M-1 (N-meso). The rate constants are large and generally parallel the stability of the adduct. The following are values of k (M-1 s-1) for addition at 25°C: CO2, 1.7 × 108 (prim-N-rac), 1.5 × 107 (N-meso); CO, 5.0 × 108 (prim-N-rac), 8.3 × 108 (N-meso); H+, 3.0 × 109 (prim-N-rac), 2.3 × 109 (N-meso).
AB - The thermodynamics and kinetics of binding of CO2, CO, and H+ to N-racemic and N-meso stereoisomers of the cobalt(I) macrocycle CoL+ (L = 5,7,7,12,14,14-hexamethyl-1,4,8,11-tetraazacyclotetradeca-4,11-diene) have been determined in aqueous media with use of the pulse radiolysis technique and transient ultraviolet-visible spectroscopy. N-rac- or N-meso-CoL+ was produced by the hydrated electron reduction of N-rac- or N-meso-CoL2+, with tert-butyl alcohol generally added to scavenge hydroxyl radicals. Reactions of both N-rac- and N-meso CoL+ are readily followed by the disappearance of intense (ε 1 × 104 M-1 cm-1) absorption bands at 630 and 635 nm, respectively. The product absorptions are much less intense (ε 200-500 M-1 cm-1) and shifted to higher energy (400-500 nm). Carbon dioxide adducts were also produced via the reactions of N-rac- or N-meso-CoL2+ with formate radical .CO2 - in solutions containing sodium formate and CO2 and hydrogen ion adducts (hydrides) by the reactions with .H atom in acid solution. The known stereochemistry of the methyl radical additions to N-rac- and N-meso-CoL2+ was used to assign the different isomers of the adducts. Thus, reaction of •H and •CO2+ with N-rac-CoL2+ yields sec-N-rac-CoL(H)2+ and sec-N-rac-CoL(CO2)+, respectively, and the reaction of N-rac-CoL+ with H+ and CO2 yields prim-N-rac-CoL(H)2+ and prim-N-rac-CoL(CO2)+, respectively. As expected, only N-meso adducts are obtained from either N-meso-CoL+ or N-meso-CoL2+. Formation constants for the complexes (determined by analysis of equilibrium absorptions or equilibration kinetics) at 25°C are CoL(CO2)+, 2.5 × 108 M-1 (prim-N-rac), 6.0 × 106 M-1 (N-meso); CoL(CO)+, 1.6 × 108 M-1 (prim-N-rac), 0.8 × 108 M-1 (N-meso); CoL(H)2+, 2.5 × 1011 M-1 (prim-N-rac), ≥7.9 × 1013 M-1 (N-meso). The rate constants are large and generally parallel the stability of the adduct. The following are values of k (M-1 s-1) for addition at 25°C: CO2, 1.7 × 108 (prim-N-rac), 1.5 × 107 (N-meso); CO, 5.0 × 108 (prim-N-rac), 8.3 × 108 (N-meso); H+, 3.0 × 109 (prim-N-rac), 2.3 × 109 (N-meso).
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M3 - Article
VL - 113
SP - 3361
EP - 3371
JO - Journal of the American Chemical Society
JF - Journal of the American Chemical Society
SN - 0002-7863
IS - 9
ER -