Abstract
The effect of pressure on proton binding to the racemic isomer of the cobalt(I) macrocycle, CoL+ (L = 5,7,7,12.-14, 14-hexamethyl-1,4,8,11-tetraazacyclotetradeca-4,11-diene), has been studied for a series of proton donors using pulse radiolysis techniques. The second-order rate constants for the reaction of CoL+ with proton donors decrease with increasing pKa of the donor acid, consistent with a reaction occurring via proton transfer. Whereas the corresponding volumes of activation (ΔV‡) are rather small and negative for all acids (proton donors) with pKa values below 8.5, significantly larger negative activation volumes are found for weaker acids (pKa> 9.5) containing OH groups as proton donors. In the latter case, the observed ΔV‡ for these protonation reactions show a correlation with the reaction volumes (ΔV°ion) for the ionization of the weak acids with a slope of 0.44, indicating that bond dissociation of the weak acid molecule bound to the metal center proceeds approximately halfway at the transition state along the reaction coordinate in terms of volume changes.
| Original language | English |
|---|---|
| Pages (from-to) | 1579-1583 |
| Number of pages | 5 |
| Journal | Inorganic Chemistry |
| Volume | 41 |
| Issue number | 6 |
| DOIs | |
| Publication status | Published - Mar 25 2002 |
Fingerprint
ASJC Scopus subject areas
- Inorganic Chemistry
Cite this
Mechanistic information from pressure acceleration of hydride formation via proton binding to a cobalt(I) macrocycle. / Fujita, Etsuko; Wishart, James F.; Van Eldik, Rudi.
In: Inorganic Chemistry, Vol. 41, No. 6, 25.03.2002, p. 1579-1583.Research output: Contribution to journal › Article
}
TY - JOUR
T1 - Mechanistic information from pressure acceleration of hydride formation via proton binding to a cobalt(I) macrocycle
AU - Fujita, Etsuko
AU - Wishart, James F.
AU - Van Eldik, Rudi
PY - 2002/3/25
Y1 - 2002/3/25
N2 - The effect of pressure on proton binding to the racemic isomer of the cobalt(I) macrocycle, CoL+ (L = 5,7,7,12.-14, 14-hexamethyl-1,4,8,11-tetraazacyclotetradeca-4,11-diene), has been studied for a series of proton donors using pulse radiolysis techniques. The second-order rate constants for the reaction of CoL+ with proton donors decrease with increasing pKa of the donor acid, consistent with a reaction occurring via proton transfer. Whereas the corresponding volumes of activation (ΔV‡) are rather small and negative for all acids (proton donors) with pKa values below 8.5, significantly larger negative activation volumes are found for weaker acids (pKa> 9.5) containing OH groups as proton donors. In the latter case, the observed ΔV‡ for these protonation reactions show a correlation with the reaction volumes (ΔV°ion) for the ionization of the weak acids with a slope of 0.44, indicating that bond dissociation of the weak acid molecule bound to the metal center proceeds approximately halfway at the transition state along the reaction coordinate in terms of volume changes.
AB - The effect of pressure on proton binding to the racemic isomer of the cobalt(I) macrocycle, CoL+ (L = 5,7,7,12.-14, 14-hexamethyl-1,4,8,11-tetraazacyclotetradeca-4,11-diene), has been studied for a series of proton donors using pulse radiolysis techniques. The second-order rate constants for the reaction of CoL+ with proton donors decrease with increasing pKa of the donor acid, consistent with a reaction occurring via proton transfer. Whereas the corresponding volumes of activation (ΔV‡) are rather small and negative for all acids (proton donors) with pKa values below 8.5, significantly larger negative activation volumes are found for weaker acids (pKa> 9.5) containing OH groups as proton donors. In the latter case, the observed ΔV‡ for these protonation reactions show a correlation with the reaction volumes (ΔV°ion) for the ionization of the weak acids with a slope of 0.44, indicating that bond dissociation of the weak acid molecule bound to the metal center proceeds approximately halfway at the transition state along the reaction coordinate in terms of volume changes.
UR - http://www.scopus.com/inward/record.url?scp=0037170868&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=0037170868&partnerID=8YFLogxK
U2 - 10.1021/ic011109q
DO - 10.1021/ic011109q
M3 - Article
VL - 41
SP - 1579
EP - 1583
JO - Inorganic Chemistry
JF - Inorganic Chemistry
SN - 0020-1669
IS - 6
ER -