Isolation and characterization of a dihydroxo-bridged iron(III,III)(μ-OH)2 diamond core derived from dioxygen.
Dioxygen addition to coordinatively unsaturated [Fe(II)(O(Me2)N4(6-Me-DPEN))](PF6) (1) is shown to afford a complex containing a dihydroxo-bridged Fe(III)2(μ-OH)2 diamond core, [Fe(III)(O(Me2)N4(6-Me-DPEN))]2(μ-OH)2(PF6)2·(CH3CH2CN)2 (2). The diamond core of 2 resembles the oxidized methane monooxygenase (MMOox) resting state, as well as the active site product formed following H-atom abstraction from Tyr-OH by ribonucleotide reductase (RNR). The Fe-OH bond lengths of 2 are comparable with those of the MMOHox suggesting that MMOHox contains a Fe(III)2(μ-OH)2 as opposed to Fe(III)2(μ-OH)(μ-OH2) diamond core as had been suggested. Isotopic labeling experiments with (18)O2 and CD3CN indicate that the oxygen and proton of the μ-OH bridges of 2 are derived from dioxygen and acetonitrile. Deuterium incorporation (from CD3CN) suggests that an unobserved intermediate capable of abstracting a H-atom from CH3CN forms en route to 2. Given the high C-H bond dissociation energy (BDE = 97 kcal/mol) of acetonitrile, this indicates that this intermediate is a potent oxidant, possibly a high-valent iron oxo. Consistent with this, iodosylbenzene (PhIO) also reacts with 1 in CD3CN to afford the deuterated Fe(III)2(μ-OD)2 derivative of 2. Intermediates are not spectroscopically observed in either reaction (O2 and PhIO) even at low-temperatures (-80 °C), indicating that this intermediate has a very short lifetime, likely due to its highly reactive nature. Hydroxo-bridged 2 was found to stoichiometrically abstract hydrogen atoms from 9,10-dihydroanthracene (C-H BDE = 76 kcal/mol) at ambient temperatures.
The Department of Chemistry, University of Washington : Box 351700 Seattle, Washington 98195-1700, United States.
Michael K
MK
Coggins
Santiago
S
Toledo
Julie A
JA
Kovacs
D018360:Crystallography, X-Ray; D018130:Diamond / Q000737:chemistry*; D005290:Ferric Compounds / Q000138:chemical synthesis / Q000737:chemistry*; D005296:Ferrous Compounds / Q000138:chemical synthesis / Q000737:chemistry; D008958:Models, Molecular; D010100:Oxygen / Q000737:chemistry*; D010105:Oxygenases / Q000737:chemistry
D005290:Ferric Compounds; D005296:Ferrous Compounds; D018130:Diamond; D010105:Oxygenases; C021555:methane monooxygenase; D010100:Oxygen