High-valent iron-oxo species are implicated as key intermediates to selectively functionalize target C-H bonds in the catalytic cycles of a range of O2-activating iron enzymes.The reactions are typically performed under ambient conditions with high efficiency and sterospecificity.Thus,elucidation of the enzymatic reaction mechanism at the atomic level should aid in designing of novel bio-inspired catalysts that are able to oxidize unactivated C-H bond under mild chemical conditions.