An Iron(III) Iodosylbenzene Complex: A Masked Non‐Heme Fe^VO

Abstract

Iodosylarenes are an important class of oxygen atom transfer reagents in organic synthesis, and they are often used in conjunction with transition-metal-based catalysts. [1][2][3] These are most commonly iron [4][5][6][7] and manganese [8][9][10][11] porphyrin, Mn-corrole, [12] Mn-corrolazinato, [13,14] and Mn-salen complexes, [15] and even cytochrome P450. [16] Hypervalent metaloxo complexes that relay the oxygen atom from the iodosylarene donor to the substrate acceptor are most commonly invoked as the active oxidants in these catalytic mechanisms. Accordingly iodsosylarenes have been used in the preparation of hypervalent metal-oxo complexes. No metal-complexed iodosylarene has been structurally characterized in the solid state; however, the isolation of a reactive iodosylbenzene complex of Mn-porphyrin was reported nearly 30 years ago. [17] Oxygen atom transfer from iodosylarenes to LM n+ complexes give the corresponding LM (n+2)+ O species (or LC + M (n+1)+ O if the ligand is non-innocent, for example when L = porphyrin) [Equation (1), steps i + ii]. Occasionally, intervening transient species assigned to metal-iodosylarene adducts have been spectroscopically identified in these types of reactions. More or less unstable Mn V O porphyrin [8] and salen [13,18,19] systems, Cr V O, [20] [(porphC)Fe IV O] +[6, 7] systems, and [Fe IV O(tmc)] 2+[21] (tmc = tetramethylcyclam) have been accessed by oxygen atom transfer from iodosylbenzene to the appropriate Mn III , Cr III , Fe III , and Fe II precursors respectively. Recently, a novel Co IV O solution species was generated at À60 8C by the reaction of 2-(tert-butylsulfonyl)iodosylbenzene with [Co II (TMG 3 tren)(OTf)] + . [22] Nam et al. have demonstrated the back-reaction of the equilibrium ii in Equation (1) by formation of a spectrosopically detected species assigned to [(porph)Fe III (OIPh)] + from the reaction of [(porphC)Fe IV O] + with iodobenzene. [6]By using the monoanionic hexadentate ligand N,N,N'tris(2-pyridylmethyl)ethylendiamine-N'-acetate (tpena À ), we describe herein the structural characterization of a reactive high-spin seven-coordinate iron(III) complex, [(tpena)Fe-(OIC 6 H 5 )] 2+ (1), which contains an auxiliary iodosylbenzene ligand. Complex 1 is prepared by dissolving the oxo-bridged complex [(tpenaH)Fe(m-O)Fe(tpenaH)] 4+ (2) in acetonitrile to form [Fe III (tpena)] 2+ (3) [Equation (2)], which then reacts with iodosylbenzene to give 1 [Equation (3)]. Dehydration and oxo bridge cleavage of 2 seems particularly facilitated by tpena À by comparison to most other oxo-bridged diiron(III) species, which are typically more robust in solution. [23,24] The uncoordinated basic pyridyl groups may be playing an active role in this process. If protonated, as is found in the crystal structure (see below), a dehydration reaction is formally intramolecular. Thus solutions of 2 turn red within minutes owing to the formation of 3, which has been characterized by ESI-MS, UV/Vis, and ESR spectroscopy. [25] The crystal structure of the Co III analogue of 3 is ...

Mononuclear Nonheme Iron(III)‐Iodosylarene and High‐Valent Iron‐Oxo Complexes in Olefin Epoxidation Reactions

“…[5,6] However, experimental and theoretical studies dispute the multiple oxidants hypothesis on the basis of the observation that iron(III)-hydroperoxo complexes are sluggish oxidants and high-valent iron-oxo porphyrin complexes can exhibit diverse reactivity patterns under different circumstances. [3,9] Thus,it is timely to investigate the reactivities of those isolated metaloxygen complexes and the mechanisms of oxidation reactions under stoichiometric conditions.F urthermore,b yc omparing the reactivities of the metal-oxygen species,the long-standing controversy on the one oxidant versus multiple oxidants hypothesis may be resolved in metal-catalyzed oxidation reactions. [3,9] Thus,it is timely to investigate the reactivities of those isolated metaloxygen complexes and the mechanisms of oxidation reactions under stoichiometric conditions.F urthermore,b yc omparing the reactivities of the metal-oxygen species,the long-standing controversy on the one oxidant versus multiple oxidants hypothesis may be resolved in metal-catalyzed oxidation reactions.…”

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

“…Compound 4 is stable for a few hours at room temperature (RT), and constitutes one of the very rare example of a iodosobenzene adduct characterized by X-ray crystallography. [7] Access to these heterometallic clusters enabled us to differentiate the Mn and Fe metal centers by both 57 Fe Mössbauer and X-ray absorption spectroscopy (XAS), giving unique insights into the structure and reactivity of 3 and 4 where coordination of iodosobenzene to low-valent Mn II is observed.…”

“…To date, only two other examples are known where iodosobenzene is bound to a biologically relevant metal (Mn or Fe), [7b,c] none of them being on a multimetallic scaffold. Furthermore, in both complexes, the iodosobenzene is bound to higher oxidation state metal centers (Fe III and Mn IV ), which are less prone to further oxidation and feature larger degrees of PhIO activation.…”

Identification and Spectroscopic Characterization of Nonheme Iron(III) Hypochlorite Intermediates

“…Thus, biomimetic model complexes provide a valuable alternative to the elucidation of the chemical nature of these intermediates. [5] The intermediacy of somewhat related Fe III -O-IPh species, which can undergo homolysis to form Fe IV =O species, is, however, precedented in the work of McKenzie and Lennartson,[6a] and Nam and co-workers,[6b,c] whereby the former study included full characterization of the intermediate using crystallography.…”