Iron(II)-induced activation of 1:1 HOOH/HCl for the chlorohydroxylation of olefins and the chlorination of hydrocarbons: Chlorinated fenton chemistry

Article abstract of DOI:10.1021/ja00106a013

Iron complexes [Fe^II(OPPh₃)₄²⁺, Fe^II(bpy)₂,²⁺, Fe^II(OH₂)₆²⁺, and Fe^IIICl₃] catalytically activate 1:1 HOOH/ HCl combinations for the efficient chlorohydroxylation of olefins. The reactive intermediate 7 is not HOCl, but appears to be formed via a Fenton process Fe^IIL_x²⁺ ? (B) [L_x⁺Fe^IIOOH(BH⁺)] (1) → (HCl) [L_xFe^IV(OH)Cl] (7) + H₂O}. Although the major product from the reaction of 7 with olefin substrates (e.g., cyclohexene, C-C₆H₁₀) is the chlorohydroxo derivative [C-C₆H₁₀ + HOOH + HCl → (Fe^IIL_x) c-C₆H₁₀(OH)Cl + H₂O], significant amounts of the dihydroxo [c-C₆H₁₀(OH)₂] and traces of the dichloro [c-C₆H₁₀Cl₂] derivatives are produced. The reaction efficiency with respect to HOOH/HC1 ranges from 51% for norbornene to 31% for cyclohexene to 10% for 1-hexene. The presence of dioxygen (O₂) with c-C₆H₁₀ results in the production of some ketone [c-C₆H₈(O)] via oxygenated Fenton chemistry, but does not inhibit the chlorohydroxylation process. The catalyzed process is equally efficient and selective in a biphasic H₂O/substrate solution as in acetonitrile. With cis-stilbene (cis-PhCH=CHPh) the major product is the epoxide (>80%); the reaction efficiency is 63% relative to HOOH/HCl. These systems chlorinate saturated hydrocarbons (c-C₆H₁₂ → c-C₆H₁₁Cl) and hydroxylate benzene (PhH → PhOH). Because 7 chlorohydroxylates olefins and chlorinates hydrocarbons in aqueous media much more efficiently than HOCl, its in-vivo analogue may be a reasonably reactive intermediate for "oxy-radical" damage in biological systems.