Tunneling in C-H oxidation reactions by an oxoiron(IV) porphyrin radical cation: direct measurements of very large H/D kinetic isotope effects.

ABSTRACT: Rate constants for oxidations of benzyl alcohol-d0 and -d7 by oxoiron(IV) tetramesitylporphyrin radical cation perchlorate in acetonitrile were measured in single turnover kinetic studies. The kinetic isotope effect (kH/kD) increased from 28 at 23 degrees C to 360 at -30 degrees C due to extensive hydrogen atom tunneling that was analyzed in terms of a parabolic energy barrier to tunneling. Similarly, large KIE values were found for oxidations of ethylbenzene-d0 and -d10 at room temperature. The large KIE values are a function of the porphyrin identity, and porphyrins containing electron-withdrawing groups display normal KIEs. KIEs found under catalytic turnover conditions are somewhat smaller than those obtained in single turnover reactions. The results should serve as benchmarks for comp

SUBMITTER: Pan Z 

PROVIDER: S-EPMC2642477 | biostudies-literature | 2008 Jun

REPOSITORIES: biostudies-literature