Kinetics of proton-coupled electron-transfer reactions to the manganese-oxo "cubane" complexes containing the Mn4O4(6+) and Mn4O4(7+) core types.

ABSTRACT: The kinetics of proton-coupled electron-transfer (pcet) reactions are reported for Mn(4)O(4)(O(2)PPh(2))(6), 1, and [Mn(4)O(4)(O(2)PPh(2))(6)](+), 1(+), with phenothiazine (pzH). Both pcet reactions form 1H, by H transfer to 1 and by hydride transfer to 1(+). Surprisingly, the rate constants differ by only 25% despite large differences in the formal charges and driving force. The driving force is proportional to the difference in the bond-dissociation energies (BDE >94 kcalmol for homolytic, 1H --> H + 1, vs. approximately 127 kcalmol for heterolytic, 1H --> H(-) + 1(+), dissociation of the OH bond in 1H). The enthalpy and entropy of activation for the homolytic reaction (deltaH = -1.2 kcalmol and deltaS= -32 calmol.K; 25-6.7 degrees C) reveal a low activation barrier and an appreciable en

SUBMITTER: Maneiro M 

PROVIDER: S-EPMC152986 | biostudies-literature | 2003 Apr

REPOSITORIES: biostudies-literature