ACTIVATION OF ALKANES - THE BIOMIMETIC APPROACH

Two kinds of biomimetic systems based on metalloporphyrin catalysts are able to perform the selective oxidation of alkanes. The first systems associate a Fe(III) or Mn(III) porphyrin catalyst and an oxygen atom donor (PhIO, H2O2 and O2+ a reducing agent). Their mechanisms are of the monooxygenase type and involve the transfer of an oxygen atom from high-valent metal-oxo active species to the alkane. Iron porphyrins bearing electron-withdrawing substituents on the beta-pyrrole positions are highly active for alkane hydroxylation. The second systems oxidize alkanes to the corresponding ketones (and alcohols) by O2 itself, without consumption of any reducing agent, in the presence of a (porphyrin) Fe(III)-OH catalyst after photochemical or thermal activation of its Fe-OH bond. Oxidation-of alkanes by these systems seem to involve a ''dioxygenase-like'' mechanism with radicals like 'OH as active species and the intermediate formation of alkylperoxy radicals.