Detection of a transient Fe^V(O)(OH) species involved in olefin oxidation by a bio-inspired non-haem iron catalyst

Abstract

The Fe(TPA) (TPA = tris(pyridyl-2-methyl)amine) class of non-haem Fe catalysts is proposed to carry out selective hydrocarbon oxidations through the generation of high-valent iron species. Using ambient mass spectrometry, we obtain direct evidence for the formation of an Fe(O)(OH) species under catalytic conditions. In addition, O-labelling suggests that this Fe(O)(OH) species serves as the active oxidant in hydrocarbon oxidation catalysis.

Bio‐inspired Nonheme Iron Oxidation Catalysis: Involvement of Oxoiron(V) Oxidants in Cleaving Strong C−H Bonds

“…In further support, a similar isotope labeling pattern can be found for ions corresponding to the cis ‐diolate product complex obtained from olefin oxidation, [Fe III ( Me2 PyTACN)( cis ‐diolate)] + , equivalent to the adduct of the m / z 486 species with olefin substrate. These conclusions have been confirmed in room‐temperature experiments by Perry, Que and co‐workers, using a different mass spectrometric technique known as transmission mode desorption electrospray ionization mass spectrometry (TM‐DESI MS) to allow the Fe V (O)(OH) intermediates of the thoroughly studied systems 1 and 1* to be observed at ambient temperature in the mass spectrometer chamber …”

“…The water‐assisted mechanism is the first O−O bond activation pathway discovered for which definitive evidence for an Fe V =(O) oxidant could be obtained. This evidence consists of the incorporation of 18 O from labeled water into the oxidation products and subsequent observation of the labeled Fe V (O)(OH) species by mass spectrometry . More recent infrared photodissociation experiments have even been able to detect the Fe=O vibration for the putative Fe V =O oxidant, although its frequency falls within the range typical of Fe IV =O complexes.…”

Hydroxylation of Aromatics by H2O2 Catalyzed by Mononuclear Non‐heme Iron Complexes: Role of Triazole Hemilability in Substrate‐Induced Bifurcation of the H2O2 Activation Mechanism

“…Hence, tetradentate or pentadentate ligands are traditionally used, leaving, respectively,e ither two or one labiles ite(s) at the iron. Hexadentate ligands bearing al abile arm can also give access to pentadentate-like reactivities.D epending on the ligand, different types of activation mechanismsw ere proposed for the generated Fe III (OOH) intermediate, either by homolytic cleavage of the OÀOb ond, yielding{ Fe IV (O);O H C} [13,[17][18][19][20] or heterolytic cleavage, to yield Fe V (O)(OH) [9,[21][22][23][24] or Fe V (O)(OAc) when assisted by acetic acid. [25][26][27] The formation of these speciesi s dictated by the ligandb ackbone, and in turn the reactivity pattern is intimately relatedt ot he nature of the reactive species.…”

Bioinspirierte Nicht‐Häm‐Eisenoxidationskatalyse: Beteiligung von Oxoeisen(V)‐Oxidantien an der Spaltung starker C‐H‐Bindungen

“…[36] Die Aktivierung eines Eisen(III)-Peroxooder -Hydroperoxo-Zwischenprodukts durch ein zweites Eisen(III)-Zentrum ist beispiellos in der bioinspirierten Nicht-Häm-Eisenchemie und kann Auswirkungen auf die Chemie der lçslichen Methanmonooxygenase haben. [ [40] In einer sehr aktuellen Entwicklung konnten Roithovµ, Costas und Mitarbeiter in der Gasphase das Fe V (O)(OH)-Zwischenprodukt fürd as substituierte TPA-Analogon Fe II ( 5tips3 TPA) (1a)a bfangen, das sich wegen seiner Reaktionen mit Substraten und des Abfangens entsprechender Fe-Produkt-Addukte als katalytisch relevant erwiesen hat. Wichtig ist, dass die Autoren in der Lage waren, Infrarot-Photodissoziation (IRPD) in Verbindung mit Massenspektrometrie zu verwenden, um IR-Daten fürd as Fe V (O)(OH)-Ion bei m/z = 424 in der Gasphase zu erhalten.…”

“…[54,62] 18 Oa us markiertem Wasser in die Oxidationsprodukte [21] und der anschließenden massenspektrometrischen Beobachtung der markierten Fe V (O)(OH)-Spezies. [39][40][41] Neuere Infrarot-Photodissoziationsexperimente konnten sogar die Fe = O-Schwingung fürd as vermeintliche Fe V =O-Oxidans nachweisen, [41] wenngleich seine Frequenz in dem fürF e IV =O-Komplexe typischen Bereich liegt. Die Beteiligung eines eisengebundenen Wassermoleküls am geschwindigkeitsbestimmenden O-O-Bindungsspaltungsschritt wurde durch kinetische Studien weiter bestätigt.…”