Reduction of dioxygen by an NADH model compound and 1,1′-dimethylferrocene catalysed by acids in homogeneous and heterogeneous systems

Abstract

A n acid-stable N A D H model compound, 10-methyl-9,lO-dihydroacridine (AcrH,) and 1 ,I '-dimethylferrocene [Fe(C,H,Me),] are oxidized by dioxygen in the presence of HCIO, in acetonitrile and water. The acid-catalysed two-electron and four-electron reductions of dioxygen by AcrH, and [ Fe( C,H,Me),],respectively, take place more efficiently in the heterogeneous systems using solid acid catalysts [alumina, silica-alumina, HY-type zeolite, and solid superacids (ZrO, and Fe,O, treated with H2S04)] activated by calcination at various temperatures. Mechanisms of both the homogeneous and heterogeneous reduction of dioxygen by AcrH, and [ Fe( C,H,Me),] are discussed.Catalytic reduction of dioxygen has been extensively studied in electrochemical systems. ' ,However, little is known of the catalytic reduction of dioxygen by mild chemical reductants such as reduced nicotinamide adenine dinucleotide (NADH) which plays a vital role as the electron source in the respiratory chain., In the absence of an appropriate catalyst, triplet dioxygen is unreactive towards NADH or the model compounds because of spin restriction. Thus, in order to achieve the efficient reduction of dioxygen by NADH or the model compounds it is required to remove the spin restriction.We have previously reported that an acid-stable NADH model compound, 10-methyl-9,lO-dihydroacridine (AcrH,), reduces a series of aromatic aldehydes as well as p-benzoquinone derivatives in the presence of perchloric acid (HCIO,)., The reactivity of the acid catalyst may be improved by using appropriate heterogeneous catalysts, since the acid strength, as well as the acidity on the surface of solid acids, can be finely tuned by choosing an appropriate solid acid catalyst and by means of activation, eg., the calcination t e m p e r a t ~r e . ~~' In this study, we report the successful reduction of dioxygen by both a two-electron reductant (AcrH,) and a one-electron reductant [Fe(C,H,Me),] in the homogeneous and heterogeneous systems by using HCIO, and solid acid catalysts, respectively. The acid-catalysed electron transfer pathways of dioxygen, which are spin-allowed processes, in the reduction of dioxygen by AcrH, as well as by [Fe(C,H,Me),] are discussed based on the Marcus electron-transfer theory.8

Acid-Induced Mechanism Change and Overpotential Decrease in Dioxygen Reduction Catalysis with a Dinuclear Copper Complex

“…It should be noted that no oxidation of Me 2 Fc occurs by O 2 in the presence of HClO 4 without 1 , under the present experimental conditions, even though ferrocene derivatives are known to be slowly oxidized by O 2 in the presence of strong acids. 39,40 It should also be noted that the use of a non-coordinating solvent (acetone) is essential for the catalytic reduction of O 2 by Me 2 Fc with 1 in the presence of HClO 4 , because a coordinating solvent such as acetonitrile prohibits such chemistry. The k obs values were also proportional to concentrations of HClO 4 (Figures 2c and S6c) and O 2 (Figures 2d and S6d).…”

Proton-Coupled Electron Transfer in Organic Synthesis: Fundamentals, Applications, and Opportunities

“…Later Fukuzumi studied the mechanism of p –benzoquinone reductions by NADH analogues [243-244]. Kinetic experiments again revealed an increase in the rate of reduction of p –benzoquinone (Q) and analogues as a function of increasing HClO 4 concentration.…”

Hydrogen peroxide as a sustainable energy carrier: Electrocatalytic production of hydrogen peroxide and the fuel cell

“…No reduction of O 2 occurred by ferrocene derivatives such as 1,1′-dimethylferrocene [Fe(C 5 H 4 Me) 2 ] in acetonitrile (MeCN) at 298 K [26], because electron transfer from Fe(C 5 H 4 Me) 2 ( E ox = 0.26 V vs. SCE) [27] to O 2 ( E red = −0.86 V vs. SCE) [28] is highly endergonic. In the presence of HClO 4 in MeCN solvent, however, O 2 is slowly reduced by Fe(C 5 H 4 Me) 2 to produce hydrogen peroxide (H 2 O 2 ) via proton-coupled electron transfer from Fe(C 5 H 4 Me) 2 to O 2 [27].…”

“…In the presence of HClO 4 in MeCN solvent, however, O 2 is slowly reduced by Fe(C 5 H 4 Me) 2 to produce hydrogen peroxide (H 2 O 2 ) via proton-coupled electron transfer from Fe(C 5 H 4 Me) 2 to O 2 [27]. Mononuclear cobalt complexes with macrobicyclic hexamine cage ligands have been reported to act as oxygen reduction catalysts for H 2 O 2 production [29,30].…”