Accelerated Oxygen Atom Transfer and C−H Bond Oxygenation by Remote Redox Changes in Fe₃Mn‐Iodosobenzene Adducts

Abstract

We report the synthesis, characterization, and reactivity of [LFe3(PhPz)3OMn(sPhIO)][OTf]x (3: x = 2; 4: x = 3), where 4 is one of very few examples of iodosobenzene–metal adducts characterized by X-ray crystallography. Access to these rare heterometallic clusters enabled differentiation of the metal centers involved in oxygen atom transfer (Mn) or redox modulation (Fe). Specifically, 57Fe Mössbauer and X-ray absorption spectroscopy provided unique insights into how changes in oxidation state (FeIII2FeIIMnII vs. FeIII3MnII) influence oxygen atom transfer in tetranuclear Fe3Mn clusters. In particular, a one-electron redox change at a distal metal site leads to a change in oxygen atom transfer reactivity by ca. two orders of magnitude.

Tetranuclear Fe Clusters with a Varied Interstitial Ligand: Effects on the Structure, Redox Properties, and Nitric Oxide Activation

“…8 The all ferrous fluoride-bridged cluster, 1 , was synthesized via addition of a 2:1 ratio of phenylpyrazole and potassium phenylpyrazolate along with one equivalent anhydrous tetrabutylammonium fluoride to a previously reported trinuclear iron precursor ( LFe 3 (OAc)(OTf) 2 , Figure 1)) 8a, 9 . The fourth Fe equivalent was delivered as Fe(N(SiMe 3 ) 2 ) 2 to complete the tetranuclear cluster ( 1 ).…”

“…Characterization by Mössbauer spectroscopy is consistent with charge localization on each Fe center and with oxidations occurring exclusively in the basal triiron core, the apical Fe remaining Fe II (Figures S26 – S31), as observed for the μ 4 -O analogs. 8b Structural characterization by single crystal X-ray diffraction (XRD) reveals that the most oxidized cluster, 3 , displays a five coordinate apical Fe II , due to acetonitrile binding (Figure S53). Removal of this ligand under vacuum results in decomposition.…”

“…Consistent with this interpretation, μ 4 -O clusters with electron withdrawing substituents show increased coordination numbers at the apical metal. 8b …”

“…11 However, there are few examples of multinuclear mononitrosyl complexes containing nearby redox-active metal centers. 8a, 12 The clusters targeted here provide insight into the influence of neighboring metal centers on the chemistry of the metal-nitrosyl moiety. Addition of NO to compound 1 leads to the formation of the corresponding nitrosyl adduct.…”

“…Herein, we present investigations of a series of tetranuclear iron clusters containing a μ 4 -F motif, isostructural with our previously reported μ 4 -O clusters (Figure 1A). 8 These compounds allow for the evaluation of the effects of the nature of the interstitial atom on cluster properties related to the activation of a single diatomic ligand (NO).…”