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

The new ligand N3PyamideSR and its FeII complex [FeII(N3PyamideSR)]­(BF4)2 (1) are described. Reaction of 1 with PhIO at −40 °C gives metastable [FeIV(O)­(N3PyamideSR)]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, [FeII(Cl)­(N3PyamideSR)]­(BF4)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 [FeII(N3PyamideS­(O)­R)]­(BF4)2 (4). Catalytic OAT with 1 was also observed.