Electronic ménages a trois: A molecular orbital perspective of protonated ferryl intermediates and synthetic models

Presented here is a molecular orbital perspective of various S = 1 iron(IV)-hydroxo compound II intermediates as well as of synthetic heme and nonheme analogues. A key conceptual issue concerns how the iron(IV) center in these species coexists with highly reducing alkoxide, thiolate, phenolate, and hydroperoxide ligands. We suggest that a clue to this conundrum involves a three-way splitting of the spin density among the iron and two π-basic ligands, which effectively delocalizes the high positive charge away from the iron.