Iron porphyrin-induced activation of dioxygen via : (A) iron porphyrins and diphenylhydrazine for the hydroxylation of hydrocarbons ; (B) t-Butylhydroperoxide for the direct ketonization of methylenic carbon ; (C) iron porphyrins for the autooxygenation of 3-methylindole

Abstract

The combination of benzyl mercaptan (PhCH$sb2$SH) and (Cl$sb8$TPP)Fe$rmsp{III}$OH or (Cl$sb8$TPP)Fe$rmsp{III}$Cl produces (Cl$sb8$TPP)Fe$rmsp{III}$SCH$sb2$Ph (22). This species and other iron(III) complexes ((Cl$sb8$TPP)Fe$sp{rm III}$X (X = Cl, ClO$sb4$, or HO) and (TPP)Fe$sp{rm III}$X (X = Cl or ClO$sb4$)) in the presence of diphenylhydrazine (PhNHNHPh) and dioxygen (O$sb2$) act as mimics for the cyctochrome P-450 proteins to produce alcohols as the main product from cyclohexane, cyclohexene, and ethylbenzene. The intermediate responsible for hydrogen abstraction from hydrocarbons is the hydroperoxide ((Cl$sb8$TPP)Fe$rmsp{IV}$(OOH)(NPhNHPh)), 26, which has a kinetic isotope effect (k$rmsb H$/k$rmsb D$) for c-C$sb6$H$sb{12}$/c-C$sb6$D$sb{12}$ of 2.3 $pm$ 0.1, and does not produce epoxide when cyclohexene is the substrate. When 22 is the catalyst, yields are the same as for (Cl$sb8$TPP)Fe$rmsp{III}$OH, because the initial step for both species is the reduction to (Cl$sb8$TPP)Fe$rmsp{II}$(MeCN)$sb2$ by excess PhNHNHPh. t-Butylhydroperoxide (or hydrogen peroxide) reacts via nucleophilic addition to (Cl$sb8$TPP)Fe$rmsp{II}$(py)$sb2$ to form an adduct ((Cl$sb8$TPP)Fe$rmsp{II}$(py)(OOt-Bu)$sp{-}$ + pyH$sp{+}$, 31), which reacts with dioxygen to form ((Cl$sb8$TPP)Fe$rmsp{II}$(O$sb2$)(OOt-Bu)$sp{-}$ + pyH$sp{+}$, 33). The latter species is the reactive intermediate for the ketonization of methylenic carbon via the reaction with a hydrocarbon substrate (RH) to form ((Cl$sb8$TPP)Fe$rmsp{II}$(OH)(OOR), 32). The iron(II) porphyrins (TPP)Fe$rmsp{II}$(py)$sb2$ and (Cl$sb8$TPP)Fe$rmsp{II}$(py)$sb2$ are readily autoxidized in the presence of O$sb2$ and 3-methylindole (MI), in contrast to reports that this combination is a successful model for tryptophan-2,3-dioxygenase. The oxidized porphyrins ((TPP)Fe$rmsp{III}$) $sb2$O and (Cl$sb8$TPP)Fe$rmsp{III}$OH catalyze the dioxygenation of MI by O$sb2$ to form 2$spprime$-formamidoacetophenone (FA) as well as the monooxygenation products 3-methyloxindole (MOI) and 3-hydroxy-3-methylindolenine (38b) (via monooxygenation).