A Diiron Center Stabilized by a Bis‐TPA Ligand as a Model of Soluble Methane Monooxygenase: Predominant Alkene Epoxidation with H₂O₂

Abstract

Double act: The diiron(II) complex [Fe2(6‐HPA)(O)(OH2)2](ClO4)4 (1) catalyzes alkene epoxidation with H2O2 via a peroxodiiron complex. Detailed isotope‐labeling experiments with μ‐18O‐1 reveal incorporation of both oxo‐ and peroxo‐derived oxygen atoms into the epoxide reaction product (see scheme; 6‐HPA=1,2‐bis[2‐{bis(2‐pyridylmethyl)aminomethyl}‐6‐pyridyl]ethane).

Insights into the P-to-Q conversion in the catalytic cycle of methane monooxygenase from a synthetic model system

“…Thus, 1.5 oxygen atoms from H 2 O 2 and 0.5 of the oxo bridge of 1 become incorporated into 3, which implies that label scrambling very likely occurs between only 2 of the 3 oxygen atoms of 2b in the subsequent loss of water to form 3. Given that the terminal oxo should be the least basic oxygen atom on 2b, protonation would very likely occur at either the oxo bridge or the terminal hydroxide to initiate the label scrambling (29). Most significantly, the above labeling experiments demonstrate that it is possible to react a diiron(III) complex with H 2 O 2 and incorporate both its oxygen atoms into an [Fe IV 2 (-O) 2 ] core, like that of 3.…”

Reversible O2-Binding and Activation with Dicopper and Diiron Complexes Stabilized by Various Hexapyridine Ligands. Stability, Modulation, and Flexibility of the Dinuclear Structure as Key Aspects for the Dimetal/O2 Chemistry

“…36 Cyclooctene was converted to an epoxide and 1,2-cis-diol in 75 and 2% yields, respectively. The turnover number of 11 exceeded one hundred.…”

“…36 The 6-hpa ligand forms diiron(III) and diiron(II) complexes [Fe 2 (O)(OH 2 ) 2 (6-hpa)](ClO 4 ) 4 (11) and [Fe 2 (TfO) 4 (6-hpa)] (12), respectively. 36 Crystal structure of 11 is shown in Fig. 8.…”

“…ESI-MS spectrum of 11 has a major peak at m=z 1033, corresponding to {[Fe 2 (O)(OH 2 ) 2 (6-hpa)](ClO 4 ) 3 } þ , but 13 gave two major peaks at m=z 362 and 445 due to monoiron complexes and two minor peaks at m=z 923 and 1007 due to diiron complexes, clearly showing that 6-hpa specifically stabilizes the diiron core in solution. 36 Although various bis-tpa type ligands shown in Chart 5 were reported, 6-hpa seems the best ligand to obtain diiron complexes as a functional model of sMMO because it specifically stabilizes the dinuclear structure and forms a flexible structure as shown by the undistorted diiron core of 11.…”

“…In this account, we introduce our recent studies on reversible O 2 -binding by dicopper complexes and O 2 -activation by diiron complexes, in which a series of hexapyridne ligands, 1,2-bis[6-di(2-pyridyl)methyl-2-pyridyl]ethane (hexpy), 33 1,2-bis[2-di-(6-methyl-2-pyridyl)methyl-6-pyridyl]ethane (H6M4h), 34 and 1,2-bis[2-(1,1-di(6-methyl-2-pyridyl)ethyl)-6-pyridyl]ethane (M6M4h), 35 and a bis-tpa type hexapyridine ligand, 1,2-bis[2-[di(2-pyridylmethyl)aminomethyl]-6-pyridyl]ethane (6-hpa) 36 have been developed. The chemical structures of these ligands are shown in Chart 3.…”