Selective photocatalytic hydroxylation and epoxidation reactions by an iron complex using water as the oxygen source

Abstract

The iron complex [(bTAML)Fe^III–OH₂]⁻ (1) selectively catalyses the photocatalytic hydroxylation and epoxidation reactions of alkanes and alkenes, respectively, using water as the oxygen-atom source. Upon the oxidation of unactivated alkanes, which included several substrates including natural products, hydroxylation was observed mostly at the 3° C–H bonds with 3° : 2° selectivity up to ∼100 : 1. When alkenes were used as the substrates, epoxides were predominantly formed with high yields. In the presence of H₂¹⁸O, more than 90% of the ¹⁸O-labelled oxygen atoms were incorporated into the hydroxylated and epoxide product indicating that water was the primary oxygen source. Mechanistic studies indicate the formation of an active [{(bTAML)Fe^IV}₂-μ-oxo]²⁻ (2) dimer from the starting complex 1via PCET. The subsequent disproportionation of 2 upon addition of substrate, leading to the formation of Fe^V(O), renders the high selectivity observed in these reactions.