Iron-catalyzed olefin cis-dihydroxylation by H₂O₂: Electrophilic versus nucleophilic mechanisms

Previous studies have classified a series of nonheme iron catalysts for olefin cis-dihydroxylation by H₂O₂ into two groups. Complex 1, [(TPA)Fe(OTf)₂], representative of Class A catalysts, forms a low-spin Fe^III-OOH intermediate that gives rise to a high-valent Fe^V(=O)OH oxidant. The preference of this catalyst for electron-rich olefins demonstrates its electrophilic character. On the other hand, complex 2, [(6-Me₃-TPA)Fe(OTf)₂], representative of Class B catalysts, prefers instead to oxidize electron-deficient olefins, suggesting an oxidant with nucleophilic character. It is suggested that such a nucleophilic oxidant may be the high-spin Fe^III-OOH intermediate derived from 2 or the Fe^IV(=O)(•OH) species derived therefrom.