Nonheme oxoiron(IV) complexes of two pentadentate ligands, N4Py (N,N-bis(2-pyridylmethyl)-bis(2-pyridyl)methylamine) and Bn-tpen (N-benzyl-N,N′,N′-tris(2-pyridylmethyl)-1,2-diaminoethane), have been generated and found to have spectroscopic properties similar to the closely related tetradentate TPA (tris(2-pyridylmethyl)amine) complex reported earlier. However, unlike the TPA complex, the pentadentate complexes have a considerable lifetime at room temperature. This greater thermal stability has allowed the hydroxylation of alkanes with C-H bonds as strong as 99.3 kcal/mol to be observed at room temperature. Furthermore, a large deuterium KIE value is found in the oxidation of ethylbenzene. These observations lend strong credence to postulated mechanisms of mononuclear nonheme iron enzymes that invoke the intermediacy of oxoiron(IV) species.