Manganese(II) complexes with Bn-tpen as powerful catalysts of cyclohexene oxidation

Abstract

Manganese(II) complex [(Bn-tpen)MnII]2+ activated dioxygen for oxidation of cyclohexene in acetonitrile (MeCN) and methanol (MeOH). In MeCN, ketone (2-cyclohexen-1-one), alcohol (2-cyclohexen-1-ol) and small amounts of epoxide (cyclohexene oxide) were produced in this reaction, while in MeOH only ketone was formed. In the most efficient experiment, the combination of 2.5 × 10−4 mol% [(Bn-tpen)MnII]2+ and 4 M cyclohexene under dioxygen atmosphere (p O2 = 1 atm) in MeCN after 24 h of reaction, gave the TON equal to 716, and the main oxidation products were ketone (196 mM) and alcohol (147 mM), whereas epoxide was formed in insignificant amounts (15 mM). The formation of [(Bn-tpen)MnIV=O]2+ and [(Bn-tpen)MnIII–OH]2+ species was confirmed. The novelty of this work is the observation, that in both solvents, [(Bn-tpen)MnII]2+ complex is initially oxidized by t-BuOOH to produce Mn(III)-complex, which is reduced back by cyclohexene to [(Bn-tpen)MnII]2+, and the latter species is an active catalyst of c-C6H10 oxidation. Knowledge of the electrochemical properties of the system components may contribute to understanding the mechanisms involving participation of the active agents created in the system.Electronic supplementary materialThe online version of this article (doi:10.1007/s11696-017-0201-0) contains supplementary material, which is available to authorized users.

An organic hole-transporting material spiro-OMeTAD doped with a Mn complex for efficient perovskite solar cells with high conversion efficiency

“…2b and c. The electron movement from the HOMO of spiro-OMeTAD to the Mn complex enhanced the production of hole carriers in spiro-OMeTAD, which improved the conductivity of spiro-OMeTAD. [46][47][48][49]…”

‘Oxygen-Consuming Complexes’–Catalytic Effects of Iron–Salen Complexes with Dioxygen

“…However, in acetonitrile, c-C 6 H 8 (O) is the dominant product for the investigated complexes. Furthermore, we have demonstrated the manganese(II) complex with the pentadentate ligand can activate dioxygen for the oxidation of cyclohexene [54].…”

“…Cyclohexene is a compound that is frequently exploited as a model substrate in preliminary catalytic studies. Due to the presence of single C-H and double C=C bonds susceptible to oxidation, studies on its reactivity serve as a good starting point for the discussion of the reaction mechanism and reactivity of this compound as well as other chemicals [54]. Previously, we found that in acetonitrile (MeCN) labile iron(II) complexes with 2,2'-bipyridine (bpy), [Fe II (bpy) 2 2+ ] MeCN activate dioxygen for the oxidation of cyclohexene [55], to ketone and alcohol.…”

The most reactive iron and manganese complexes with N-pentadentate ligands for dioxygen activation—synthesis, characteristics, applications

“…25 °C) [ 81 ] [(Bn-TPEN)Mn II ] 2+ (1 mM)/Al(OTf) 3 (2 mM) /MeCN/CH 2 Cl 2 catalytic epoxidation of cyclooctene (0.05 M) corresponding oxide (89%), (temp. 0 °C, time: 3.5 h) [ 85 ] [(Bn-TPEN)Mn II ] 2+ (0.5–10 mM)/air or O 2 /MeCN and/or MeOH cyclohexene (1–4 M) oxidation corresponding ketone, alcohol, and epoxide; e.g cyclohexanone (12%), cyclohexenol (6%) and traces of epoxide **** [ 84 ] [(Bn-TPEN)Mn IV = O] 2+ (0.5–0.8 mM) /TFE/MeCN anthracene (0.10 mM), 9-methylanthracene (0.20 mM), 9,10-dimethylanthracene (0.25 mM) oxidation corresponding ketones – anthraquinones; e.g. anthracene was completely (100% yield) oxidized to anthraquinone (temp.…”

“…They also eliminate the need for more expensive and complex higher molecular weight porphyrin ligands [ 26 ]. [(Bn-TPEN)Mn] 2+ catalyze oxidation of cyclohexene by dioxygen to ketone and alcohol [ 84 ], and epoxidation of cyclooctene, where redox-inactive metal ions, acting as a Lewis acid in oxygen atom transfer reaction were used [ 85 ]. However, when there are no redox-inactive metal ions in the reaction medium, then the manganese(II) catalyst reacts very sluggish, (8.7% yield of epoxide), and addition of Al 3+ ions to manganese(II) complex significantly improves epoxidation (88.9% yield of epoxide) [ 85 ].…”