Reverse Catalase Reaction: Dioxygen Activation via Two-Electron Transfer from Hydroxide to Dioxygen Mediated By a Manganese(III) Salen Complex.
Although atmospheric dioxygen is regarded as the most ideal oxidant, O2 activation for use in oxygenation reactions intrinsically requires a costly sacrificial reductant. The present study investigated the use of aqueous alkaline solution for O2 activation. A manganese(III) salen complex, Mn(III)(salen)(Cl), in toluene reacts with aqueous KOH solution under aerobic conditions, which yields a di-μ-oxo dimanganese(IV) salen complex, [Mn(IV)(salen)]2(μ-O)2. The (18)O isotope experiments show that (18)O2 is indeed activated to give [Mn(IV)(salen)]2(μ-(18)O)2 via a peroxide intermediate. Interestingly, the (18)OH(-) ion in H2(18)O was also incorporated to yield [Mn(IV)(salen)]2(μ-(18)O)2, which implies that a peroxide species is also generated from (18)OH(-). The addition of benzyl alcohol as a stoichiometric reductant selectively inhibits the (18)O incorporation from (18)OH(-), indicating that the reaction of Mn(III)(salen)(Cl) with OH(-) supplies the electrons for O2 reduction. The conversion of both O2 and OH(-) to a peroxide species is exactly the reverse of a catalase-like reaction, which has a great potential as the most efficient O2 activation. Mechanistic investigations revealed that the reaction of Mn(III)(salen)(Cl) with OH(-) generates a transient species with strong reducing ability, which effects the reduction of O2 by means of a manganese(II) intermediate.
Institute for Molecular Science, National Institutes of Natural Sciences , Myodaiji, Okazaki, Aichi 444-8787, Japan.
Takuya
T
Kurahashi
D002374:Catalase / Q000737:chemistry / Q000378:metabolism*; D004579:Electron Transport; D005029:Ethylenediamines / Q000737:chemistry / Q000378:metabolism*; D006878:Hydroxides / Q000737:chemistry / Q000378:metabolism*; D008345:Manganese / Q000737:chemistry / Q000378:metabolism*; D015394:Molecular Structure; D009942:Organometallic Compounds / Q000737:chemistry / Q000378:metabolism*; D010100:Oxygen / Q000737:chemistry / Q000378:metabolism*
D005029:Ethylenediamines; D006878:Hydroxides; D009942:Organometallic Compounds; D008345:Manganese; C031356:hydroxide ion; C011452:disalicylaldehyde ethylenediamine; D002374:Catalase; D010100:Oxygen