Dramatically Accelerated Selective Oxygen-Atom Transfer by a Nonheme Iron(IV)-Oxo Complex: Tuning of the First and Second Coordination Spheres

[Image: see text] The new ligand N3Py(amide)SR and its Fe(II) complex [Fe(II)(N3Py(amide)SR)](BF(4))(2) (1) are described. Reaction of 1 with PhIO at −40 °C gives metastable [Fe(IV)(O)(N3Py(amide)SR)](2+) (2), containing a sulfide ligand and a single amide H-bond donor in proximity to the terminal oxo group. Direct evidence for H-bonding is seen in a structural analogue, [Fe(II)(Cl)(N3Py(amide)SR)](BF(4))(2) (3). Complex 2 exhibits rapid O-atom transfer (OAT) toward external sulfide substrates, but no intramolecular OAT. However, direct S-oxygenation does occur in the reaction of 1 with mCPBA, yielding sulfoxide-ligated [Fe(II)(N3Py(amide)S(O)R)](BF(4))(2) (4). Catalytic OAT with 1 was also observed.