Kinetics and mechanism of oxygen transfer in the reaction of p-cyano-N,N-dimethylaniline N-oxide with metalloporphyrin salts. 5. The influence of imidazole ligation of (meso-tetrakis(2,6-dimethylphenyl)porphinato)manganese(III) chloride on the rates of oxygen transfer from N-oxide to metalloporphyrin salt and the efficiency of oxidations by the intermediate higher valent manganese-oxo species
Equilibrium constants for mono- and bisligation of imidazole (ImH) with (meso-tetrakis(2,6-dimethylphenyl)porphinato)manganese(III) chloride ((Me/sub 8/TPP)Mn/sup III/Cl) have been determined so that the concentrations (dry CH/sub 2/Cl/sub 2/) of the three species (Me/sub 8/TPP)Mn/sup III/Cl, ((Me/sub 8/TPP)Mn/sup III/(ImH))Cl, and ((Me/sub 8/TPP)Mn/sup III/(ImH)/sub 2/)Cl may be calculated at different ImH concentrations. The equilibrium constants for ligation of the one and two imidazoles are K/sub 1/ = 245 M/sup -1/ and ..beta../sub 2/ = 1.80 x 10/sup 5/ M/sup -1/. The reaction of p-cyano-N,N-dimethylaniline N-oxide (NO) with the manganese(III)porphyrin (under the pseudo-first-order conditions of (NO)/sub i/ >> ((Me/sub 8/TPP)Mn/sup III/Cl)/sub i/ and in the presence and absence of ImH) is first order in both NO and manganese(III) porphyrin, and the rate-controlling step involves oxygen transfer with formation of higher valent manganese-oxo porphyrin species plus p-cyano-N,N-dimethylaniline (DA). From the dependence of the pseudo-first-order rate constants (k/sub obsd/) upon (ImH)/sub i/ and a knowledge of the equilibrium constants for imidazole ligation there has been calculated the second-order rate constants for the kinetic terms k/sub 1/(NO)((Me/sub 8/TPP)Mn/sup III/Cl), k/sub 2/(NO)((Me/sub 8/TPP)Mn/sup III/(ImH))Cl, and k/sub 3/(NO)((Me/sub 8/TPP)Mn/sup III/(ImH)/sub 2/)Cl). Comparison of the second-order rate constants (k/sub 1/ = 3.3 x 10/sup -2/ M/sup -1/ s/sup -1/, k/sub 2/ = 5.53 M/sup -1/ s/sup -1/, and k/sub 4/ = 7.32 x 10/sup -2/ M/sup -1/ s/sup -1/) establishes that ligation by one imidazole increases the rate of reaction of the manganese(III) porphyrin with NO by approx. 166-fold.
- Research Organization:
- Univ. of California, Santa Barbara
- OSTI ID:
- 6368220
- Journal Information:
- J. Am. Chem. Soc.; (United States), Vol. 109:11
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
ORGANIC
PHYSICAL AND ANALYTICAL CHEMISTRY
CHLORIDES
CHEMICAL REACTIONS
IMIDAZOLES
MANGANESE COMPOUNDS
NITRIC OXIDE
ORGANOMETALLIC COMPOUNDS
PORPHYRINS
ALKENES
CHEMICAL REACTION KINETICS
EPOXIDES
EQUILIBRIUM
EXPERIMENTAL DATA
OXYGEN
QUANTITY RATIO
REACTION INTERMEDIATES
AZOLES
CARBOXYLIC ACIDS
CHALCOGENIDES
CHLORINE COMPOUNDS
DATA
ELEMENTS
HALIDES
HALOGEN COMPOUNDS
HETEROCYCLIC ACIDS
HETEROCYCLIC COMPOUNDS
HYDROCARBONS
INFORMATION
KINETICS
NITROGEN COMPOUNDS
NITROGEN OXIDES
NONMETALS
NUMERICAL DATA
ORGANIC ACIDS
ORGANIC COMPOUNDS
ORGANIC NITROGEN COMPOUNDS
ORGANIC OXYGEN COMPOUNDS
OXIDES
OXYGEN COMPOUNDS
REACTION KINETICS
TRANSITION ELEMENT COMPOUNDS
400201* - Chemical & Physicochemical Properties