Di-μ-oxo Dimetal Core of MnIV and TiIV as a Linker Between Two Chiral Salen Complexes Leading to the Stereoselective Formation of Different M- and P-Helical Structures

Crystal structure of (((1E,1′E)-(cyclohexane-1,2-diylbis(azanylylidene-κ2 N,N′))bis(methanylylidene))bis(2,1-phenylene))bis((2,6-diisopropylphenyl)amide-κ2 N′′,N′′′)manganese(II), C44H54N4Mn

C44H54N4Mn, monoclinic, C2/c (no. 15), a = 15.315(3) Å, b = 14.259(3) Å, c = 18.118(3) Å, β = 105.252(3)°, V = 3817.1(12) Å3, Z = 8, R gt (F) = 0.0472, wR ref (F 2 ) = 0.1287, T = 185 K.

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.

Visible-light activation of the bimetallic chromophore-catalyst dyad: analysis of transient intermediates and reactivity toward organic sulfides

In order to develop a new photocatalytic system, we designed a new redox-active module (5) to hold both a photosensitizer part, [Ru(II)(terpy)(bpy)X](n+) (where terpy = 2,2':6',2''-terpyridine and bpy = 2,2'-bipyridine), and a popular Jacobsen catalytic part, salen-Mn(III), covalently linked through a pyridine-based electron-relay moiety. On the basis of nanosecond laser flash photolysis studies, an intramolecular electron transfer mechanism from salen-Mn(III) to photooxidized Ru(III) chromophore yielding the catalytically active high-valent salen-Mn(IV) species was proposed. To examine the reactivity of such photogenerated salen-Mn(IV), we employed organic sulfide as substrate. Detection of the formation of a Mn(III)-phenoxyl radical and a sulfur radical cation during the course of reaction using time-resolved transient absorption spectroscopy confirms the electron transfer nature of the reaction. This is the first report for the electron transfer reaction of organic sulfide with the photochemically generated salen-Mn(IV) catalytic center.