| 16411722 |
Carson EC, Lippard SJ: Dioxygen-initiated oxidation of heteroatomic substrates incorporated into ancillary pyridine ligands of carboxylate-rich diiron (II) complexes. Inorg Chem. 2006 Jan 23;45(2):837-48.
Progress toward the development of functional models of the carboxylate-bridged diiron active site in soluble methane monooxygenase is described in which potential substrates are introduced as substituents on bound pyridine ligands. Pyridine ligands incorporating a thiol, sulfide, sulfoxide, or phosphine moiety were allowed to react with the preassembled diiron (II) complex [Fe (2)(mu-O (2) CAr (R))(2)(O (2) CAr (R))(2)(THF)(2)], where (-) O (2) CAr (R) is a sterically hindered 2,6-di (p-tolyl)- or 2,6-di (p-fluorophenyl) benzoate (R = Tol or 4-FPh). The resulting diiron (II) complexes were characterized crystallographically. Triply and doubly bridged compounds [Fe (2)(mu-O (2) CAr (Tol))(3)(O (2) CAr (Tol))(2-MeSpy)] (4) and [Fe (2)(mu-O (2) CAr (Tol))(2)(O (2) CAr (Tol))(2)(2-MeS (O) py)(2)] (5) resulted when 2-methylthiopyridine (2-MeSpy) and 2-pyridylmethylsulfoxide (2-MeS (O) py), respectively, were employed. Another triply bridged diiron (II) complex, [Fe (2)(mu-O (2) CAr (4)(-)(FPh))(3)-(O (2) CAr (4)(-)(FPh))(2-Ph (2) Ppy)] (3), was obtained containing 2-diphenylphosphinopyridine (2-Ph (2) Ppy). The use of 2-mercaptopyridine (2-HSpy) produced the mononuclear complex [Fe (O (2) CAr (Tol))(2)(2-HSpy)(2)] (6a). Together with that of previously reported [Fe (2)(mu-O (2) CAr (Tol))(3)(O (2) CAr (Tol))(2-PhSpy)] (2) and [Fe (2)(mu-O (2) CAr (Tol))(3)(O (2) CAr (Tol))(2-Ph (2) Ppy)] (1), the dioxygen reactivity of these iron (II) complexes was investigated. A dioxygen-dependent intermediate (6b) formed upon exposure of 6a to O (2), the electronic structure of which was probed by various spectroscopic methods. Exposure of 4 and 5 to dioxygen revealed both sulfide and sulfoxide oxidation. Oxidation of 3 in CH (2) Cl (2) yields [Fe (2)(mu-OH)(2)(mu-O (2) CAr (4)(-)(FPh))(O (2) CAr (4)(-FPh))(3)(OH (2))(2-Ph (2 ) P (O) py)] (8), which contains the biologically relevant {Fe (2)(mu-OH)(2)(mu-O (2) CR)}(3+) core. This reaction is sensitive to the choice of carboxylate ligands, however, since the p-tolyl analogue 1 yielded a hexanuclear species, 7, upon oxidation. |
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