Intrinsic Kinetic Selectivities in the Photooxidation of Organic Substrates by aRange of Polyoxometalates Varying in Redox Potential

摘要

The data from 4 types of experiments are consistent with radical abstraction,usually rate limiting, as the dominant general mode of reaction of excited state polyoxometalates with organic substrates: the relative rates and quantum yields for oxidation of cyclohexane and cyclohexanol by several polyoxometalates varying widely in ground state redox potential from approx. OV (very irreversible) vs Ag+/Ag in CH3CN for (V sub 10 O sub 28(6-) to -1.3 V for W sub 10 O sub 32(4-)) the relative reactivities of several cyclohexyl and cyclooctyl derivatives with excited (W sub 10 O sub 32(4-) and with an authentic ground state organic radical, t-butoxyl, the excellent correlation between the relative rates for reaction of excited (W sub 10 O 32(4-) and cycloalkanes with the C-H bond energies of the substrates, and the product distributions generated on oxidation of five representative substrates by excited (W sub 10 O 32(4-). The collective data, however, do not rule out other mechanisms for some reactions between excited state polyoxometalates and organic substrates.