title: An Ultra-Stable Oxoiron(IV) Complex and Its Blue Conjugate Base.
abstract: Treatment of [FeII(L)](OTf)2(4), (whereL= 1,4,8-Me3cyclam-11-CH2C(O)NMe2) with iodosylbenzene yielded the correspondingS= 1 oxoiron(IV) complex [FeIV(O(L)](OTf)2(5) in nearly quantitative yield. The remarkably high stability of5(t1/2≈ 5 days at 25 °C) facilitated its characterization by X-ray crystallography and a raft of spectroscopic techniques. Treatment of5with strong base was found to generate a distinct, significantly less stableS= 1 oxoiron(IV) complex,6(t1/2~ 1.5 hrs. at 0 °C), which could be converted back to5by addition of a strong acid; these observations indicate that5and6represent a conjugate acid-base pair. That6can be formulated as [FeIV(O)(L-H)](OTf) was further supported by ESI mass spectrometry, spectroscopic and electrochemical studies, and DFT calculations. The close structural similarity of5and6provided a unique opportunity to probe the influence of the donortransto the FeIV=O unit upon its reactivity in H-atom transfer (HAT) and O-atom transfer (OAT), and5was found to display greater reactivity than6in both OAT and HAT. While the greater OAT reactivity of5is expected on the basis of its higher redox potential, its higher HAT reactivity does not follow the anti-electrophilic trend reported for a series of [FeIV(O)(TMC)(X)] complexes (TMC = tetramethylcyclam) and thus appears to be inconsistent with the Two-State Reactivity rationale that is the prevailing explanation for the relative facility of oxoiron(IV) complexes to undergo HAT.
authors.affiliation: Department of Chemistry and Center for Metals in Biocatalysis, University of Minnesota, 207 Pleasant St. SE, Minneapolis, Minnesota 55455, USA.
authors.forename: Jason
authors.initials: J
authors.lastname: England
authors.affiliation: Department of Chemistry and Center for Metals in Biocatalysis, University of Minnesota, 207 Pleasant St. SE, Minneapolis, Minnesota 55455, USA.
authors.forename: Jennifer O
authors.initials: JO
authors.lastname: Bigelow
authors.affiliation: Department of Chemistry and Center for Metals in Biocatalysis, University of Minnesota, 207 Pleasant St. SE, Minneapolis, Minnesota 55455, USA.
authors.forename: Katherine M
authors.initials: KM
authors.lastname: Van Heuvelen
authors.affiliation: Department of Chemistry and Center for Metals in Biocatalysis, University of Minnesota, 207 Pleasant St. SE, Minneapolis, Minnesota 55455, USA.
authors.forename: Erik R
authors.initials: ER
authors.lastname: Farquhar
authors.affiliation: Department of Chemistry, Carnegie Mellon University, 4400 5 Ave., Pittsburgh, PA 15213, USA.
authors.forename: Marléne
authors.initials: M
authors.lastname: Martinho
authors.affiliation: Department of Chemistry, Carnegie Mellon University, 4400 5 Ave., Pittsburgh, PA 15213, USA.
authors.forename: Katlyn K
authors.initials: KK
authors.lastname: Meier
authors.affiliation: Department of Chemistry and Center for Metals in Biocatalysis, University of Minnesota, 207 Pleasant St. SE, Minneapolis, Minnesota 55455, USA.
authors.forename: Jonathan R
authors.initials: JR
authors.lastname: Frisch
authors.affiliation: Department of Chemistry, Carnegie Mellon University, 4400 5 Ave., Pittsburgh, PA 15213, USA.
authors.forename: Eckard
authors.initials: E
authors.lastname: Münck
authors.affiliation: Department of Chemistry and Center for Metals in Biocatalysis, University of Minnesota, 207 Pleasant St. SE, Minneapolis, Minnesota 55455, USA.
authors.forename: Lawrence
authors.initials: L
authors.lastname: Que