Reverse Catalase Reaction: Dioxygen Activation via Two-Electron Transfer from Hydroxide to Dioxygen Mediated By a Manganese(III) Salen Complex

Abstract

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.

Synthesis, Electronic, Magnetic and Structural Characterization of New Trinuclear Mixed‐Valence CoIII‐CoII‐CoIII Complex.

“…Indeed, the pH‐controlled protonation or deprotonation of the phenolic groups gives the possibility to obtain compounds with different numbers of metal centres and coordination geometries, giving rise to synthesis of homometallic or heterometallic complexes . These compounds are also of interest for their catalytic properties and as models of biological systems …”

“…[19] These compounds are also of interest for their catalytic properties [20] and as models of biological systems. [21][22][23] Herein we report the synthesis, structure, electronic and magnetic properties of a trinuclear mixed-valence Co II,III complex using acetate and a derivative of H 2 Salen, namely N,N'-bis(salicylidene)-2-hydroxy-1,3-propanediamine, abbreviated H 3 L hereafter, where H represents dissociable hydroxy H atoms. The structure refinement of this complex, [Co 3 (HL) 2 (m-AcO) 2 (AcO) 2 ] proved to be challenging, because of the very low scattering power of the crystallized sample.…”

Drastic Redox Shift and Electronic Structural Changes of a Manganese(III)-Salen Oxidation Catalyst upon Reaction with Hydroxide and Cyanide Ion

“…Autoreduction of a metal complex is not necessarily limited to the porphyrin system, but was also reported for a bis­(benzene-1,2-dithiolato) copper­(III) complex . Another interesting example is an antimony­(V) porphyrin bearing hydroxide axial ligands, which is reduced upon photoirradiation. , I also reported that the reaction of a manganese­(III) salen complex with aqueous alkaline solution yields a manganese­(II)–manganese­(III) dimer …”

The concept of photochemical enzyme models – State of the art

“…Although oxidoreductases capable of direct interaction with O 2 in its triplet ground state have been identified [85], the majority of native oxidase enzymes requires additional organic cofactors or redox-active transition metal centers Molecular oxygen from air is a clean, abundant and environmentally benign reagent ideally suited for substrate oxidation processes including selective C-H bond functionalization. Therefore the utilization of oxidase-like reactivity for green synthetic processes based on O 2 or H 2 O 2 is a highly desirable research goal [92][93][94].…”