Biomimetic nonheme iron catalysts for alkane hydroxylation

The catalytic functionalization of alkanes under mild conditions is a subject of great current interest. Nature has evolved a number of metalloenzymes such as the heme-containing cytochrome P450 and the nonheme methane monooxygenase, which are capable of effecting such transformations. There has thus been significant interest in modeling such enzyme active sites and developing biomimetic alkane hydroxylation catalysts. In this review, the efforts of the last 10 years in the development of nonheme iron catalysts are summarized and discussed. These catalysts typically act in concert with ROOH or H2O2. With ROOH as oxidant, it is clear from mechanistic studies that alkoxyl radicals are the principal agents that cleave the alkane C-H bond to generate long-lived alkyl radicals. This conclusion, for the most part, applies also for oxidations involving H2O2. In a few cases, however, stereospecific alkane hydroxylation is observed. For these instances, there is evidence from (H2O)-O-18 exchange experiments that a high-valent iron-ore species is involved. (C) 2000 Elsevier Science S.A. All rights reserved.