Aerobic Catechol Oxidation Catalyzed by a Bis(μ-oxo)dimanganese(III,III) Complex via a Manganese(II)−Semiquinonate Complex

Abstract

A 3,5-di-tert-butyl-1,2-semiquinonato (DTBSQ) adduct of Mn(II) was prepared by a reaction between Mn(II)(TPA)Cl(2) (TPA = tris(pyridin-2-ylmethyl)amine) and DTBSQ anion and was isolated as a tetraphenylborate salt. The X-ray crystal structure revealed that the complex is formulated as a manganese(II)-semiquinonate complex [Mn(II)(TPA)(DTBSQ)](+) (1). The electronic spectra in solution also indicated the semiquinonate coordination to Mn. The exposure of 1 in acetonitrile to dioxygen afforded 3,5-di-tert-butyl-1,2-benzoquione and a bis(mu-oxo)dimanganese(III,III) complex [Mn(III)(2)(mu-oxo)(2)(TPA)(2)](2+) (2). The reaction of 2 with 3,5-di-tert-butylcatechol (DTBCH(2)) quantitatively afforded two equivalents of 1 under anaerobic conditions. The highly efficient catalytic oxidation of DTBCH(2) with dioxygen was achieved by combining the above two reactions, that is, by constructing a catalytic cycle involving both manganese complexes 1 and 2. It was revealed that dioxygen is reduced to water but not to hydrogen peroxide in the catalytic cycle.

Redox‐Induced μ‐Acetato and μ‐Oxo Core Interconversions in Dinuclear Manganese Tris(2‐methylpyridyl)amine (tpa) Complexes: Isolation and Characterization of [Mn2III(μ‐O)(μ‐O2CCH3)(tpa)2]3+

“…The green (IV,IV) complex 3 4+ (spectrum c) exhibits three visible bands at 418, 534 and 642 nm. This spectrum is similar to that obtained by Suzuki et al [38] [ 36] www.eurjic.org The reduction wave, which is only partially reversible at that scan rate, is associated with the redox states Mn 2 III,III/III,II [Equation (5)]. …”

“…[bpia = bis(picolyl)(N-methylimidazol-2-yl)-amine] [41] the two manganese ions are separated by 3.250(1) and 3.2544(8) Å, respectively. Compared to the other crystallographically characterized dimanganese tpa complexes, the Mn···Mn distance in 2 3+ is significantly longer than those found in the bis(µ-oxo) complexes at the (III,III) and (III,IV) oxidation level [2.656(2) Å (3 2+ ) [36] and 2.643(1) Å (3 3+ ) [37] ] and shorter than that in the bis(µ-acetato) complex [4.154 (1) [39][40][41] The Mn-N pyridine (4 and 8) bonds ( Table 1); the theoretical value is 90°.…”

“…[23] µ-Acetato/µ-hydroxo or µ-oxo bridging ligand changes in relation to Mn oxidation have been reported for synthetic binuclear Mn complexes with multidentate ancillary N and/ or O ligands. [24][25][26][27][28][29][30][31][32][33][34] Electrochemistry is a convenient way to investigate these kinds of redox-induced structural changes, and we have previously demonstrated the efficiency of the electrochemically induced core interconversion in an organic medium (CH 3 [35][36][37] have been structurally and spectroscopically characterized previously, and the electrochemical properties of 3 3+ have been briefly studied in CH 3 CN. [37,38] In contrast, complex 2 3+ , which possesses a rare mono-(µ-oxo) mono-(µ-acetato) motif, [39][40][41] has not been isolated previously and we report here its characterization by X-ray crystallography.…”

Synthesis, properties, and catecholase-like activity of the [1,4-di(6′-methyl-2′-pyridyl)aminophthalazine]dimanganese(II) complex, Mn2(6′Me2PAP)2Cl4

“…The results are V max = 42.9 · 10 )7 mol dm )3 s )1 , K M = 6.4· 10 )3 mol dm )3 , k cat = 46.6· 10 )3 s )1 and k 2 (k cat /K M ) = 7.25 mol )1 dm )3 s )1 . The turnover rate of 167.9h )1 is comparable to those values reported for the mononuclear Mn III (k cat = 86-336h )1 ) [26,27], but significantly lower than those recently reported for the binuclear Mn IV (k cat = 940-1620h )1 ) complexes [14].…”

Structure, magnetic properties, catalase activity and DFT studies of [Mn2(μ-RCOO)2(μ-OR)2]2+ type dinuclear manganese(III,III) complexes

“…A variety of Mn(III,III) complexes differing in their core units have been reported so far (Scheme 1). The core structures and observed MnÁ Á ÁMn distances of oxo-and alkoxo-bridged dimanganese(III,III) complexes are as follows: Type-I, [Mn 2 (l-OR) 2 ] 4+ , 3.00-3.04 Å [7][8][9][10][11][12][13][14][15]; Type-II, [Mn 2 (l-RCOO)(l-OR) 2 ] 3+ , 2.91-2.94 Å [16][17][18][19][20][21][22][23]; Type-III, [Mn 2 (l-RCOO) 2 (l-OR) 2 ] 2+ , 2.85-2.87 Å [24][25][26][27][28]; Type-IV, [Mn 2 O 2 ] 2+ , 2.64-2.75 Å [29][30][31][32][33][34][35][36]; Type-V, [Mn 2 (l-RCOO) 2 (l-O)] 2+ , 3.08-3.22 Å [37][38][39][40][41][42][43][44][45][46][47][48]. The first four types form complexes with coplanar equatorial planes and parallel Jahn-Teller axes, while in Type-V complexes the Jahn-Teller axes were inclined by 27-90°.…”