Design and Fine-Tuning Redox Potentials of Manganese(II) Complexes with Isoindoline-Based Ligands: H2O2 Oxidation and Oxidative Bleaching Performance in Aqueous Solution

Abstract

A series of divalent manganese complexes [M II (HL 1-6 )Cl 2 ] with the 1,3-bis(2'-Ar-imino) isoindolines (HL n , n = 1-6, Ar = pyridyl, 4-methylpyridyl, imidazolyl, thiazolyl, benzimidazolyl and N-methylbenzimidazolyl, respectively) including the previously reported ligands (HL 1-2, 4-6 ) and complexes ([M II (HL 1,5 )Cl 2 ]) have been prepared and characterized by electrochemical and spectroscopic methods. In these complexes, it was possible to control the redox potential of the metal center by varying the aryl substituent on the bis-iminoisoindoline moiety, and investigate its effect in a catalase-like reaction, and oxidative bleaching process in buffered aqueous solution. The kinetics of the dismutation of H 2 O 2 into H 2 O and O 2 , and the oxidative degradation of morin by H 2 O 2 were investigated in buffered water, where the reactivity of the catalysts in both systems was markedly influenced by the redox and Lewis acidic properties of the metal centers and the concentration of the bicarbonate ions. Both the catalase-like and bleaching activity of the catalysts showed a linear correlation with the Mn III /Mn II redox potentials. The E 1/2 spans a 561 mV range from 388 mV (Ar = benzymidazolyl) to 948 mV (Ar = 4-methylpyridyl) vs. the SCE. The amount of bicarbonate is a critical issue for the in situ formation of peroxycarbonate as a versatile oxidant, and its participation in the formation of high valent Mn IV = O species.

Synthesizing environmentally friendly non-silicone oxygen bleaching stabilizer for linen yarn using oligomeric acrylic acid

“…When potassium persulfate increased to 5% of the mass of acrylic acid, the chelated iron value reached the maximum, it indicated that the amount of initiator met the requirements of the polymerization, and the number of free radicals generated was enough to initiate the monomer polymerization. The potassium persulfate dosage increased to 6%, the chelated iron value decreased significantly, indicated that excessive initiator increased the crosslinking degree of monomers, decreased the sensitivity and reduced the chelating performance 33 . The chelated calcium value hardly fluctuated, indicating that initiator dosage had little effect on chelated calcium value.…”

Effect of redox potential on manganese-mediated benzylalcohol and sulfide oxidation

“…The ligands 1,3-bis(2 -Ar-imino)isoindolines (HL n , n = 1-6, Ar = 4 -methyl-pyridyl, pyridyl, imidazolyl, thiazolyl, benzimidazolyl and Nmethylbenzimidazolyl, respectively) and their complexes [Mn II (HL 1−6 )Cl 2 ] (1-6) were prepared according to published procedures (Scheme 1) [12,18]. GC analyses were performed on an Agilent 6850 gas chromatograph equipped with a flame ionization detector and 30 m SUPELCO BETA DEX225 columns.…”

“…Based on our previous experience we expected that varying the aryl group on the bisiminoisoindoline moiety would directly tune electron density in the metal center and hence allow us to evaluate the influence of these electronic changes on reactivity. Cyclic voltammetry measurements on complexes 1-6 reveal that the Mn(III/II) redox potentials can vary by up to 560 mV between the most electron-withdrawing (948 mV for 1) and the most electron-donating (388 mV for 5) [18]. With a systematic series of [Mn II (HL 1−6 )Cl 2 ] (1-6) complexes, we investigated their oxidative reactivity for HAT (hydrogen atom transfer) and OAT (oxygen atom transfer) reactions with benzyl alcohol and thioanisole.…”

“…These enzymes catalyze many oxidation reactions including oxygen atom transfer (hydroxylation, epoxidation) and dealkylation, but much less activation was observed when iron was replaced by manganese. However, in biomimetic systems oxomanganese complexes mediate most of the oxidations brought by the iron oxygenases leading to a wide range of manganese be used as hydrogen peroxide-based bleach catalysts [18]. In this ligand the introduction of various aryl groups on the bis-iminoisoindoline moiety provided a new method for tuning the reactivity and electronic structure of the catalyst.…”

“…a Reaction conditions: Thioanisole (1.5 mmol), catalyst (0.03 mmol), oxidant (0.75 mmol) in MeCN (3 ml) at 25°C. b mV versus SCE[18]. c TON = mol S/mol Cat.…”