Direct Selective Oxidative Functionalization of C–H Bonds with H2O2: Mn-Aminopyridine Complexes Challenge the Dominance of Non-Heme Fe Catalysts

Abstract

Non-heme iron(II) complexes are widespread synthetic enzyme models, capable of conducting selective C-H oxidation with H 2 O 2 in the presence of carboxylic acid additives. In the last years, structurally similar manganese(II) complexes have been shown to catalyze C-H oxidation with similarly high selectivity, and with much higher efficiency. In this mini-review, recent catalytic and mechanistic data on the selective C-H oxygenations with H 2 O 2 in the presence of manganese complexes are overviewed. A distinctive feature of catalyst systems of the type Mn complex/H 2 O 2 /carboxylic is the existence of two alternative reaction pathways (as found for the oxidation of cumenes), one leading to the formation of alcohol, and the other to ester. The mechanisms of formation of the alcohol and the ester are briefly discussed.

Efficient Aliphatic C−H Bond Oxidation Catalyzed by Manganese Complexes with Hydrogen Peroxide

“…Thus, the CÀHo xidation of cyclohexane was carried out under higheri njection of 3.5 equivalents of H 2 O 2 ,w hichw as widely adopted in the methylene oxidation. [13, 15k, 21] As ar esult,b oth conversions were improved, giving higher yields and selectivities ( Table 1, entries [3][4]. Based on the preliminary results, the catalyst C1 exhibited better catalytic activity than C2 ( Table 1, entries 1-2).…”

“…In both cases of adamantane, adamantane-1,3-diol was obtained( Table 4, entries 1-2). [26] Then, the enantiomers of menthyl acetate were also investigated in the establishedm anganesec omplex catalyzed CÀHo xidation ( Table 4, entries [3][4]. The resultss howed that (1 S)-(+ +)-menthyl acetate exhibited highera ctivity than (1 R)-(À)-menthyl acetate under this cata- Figures S1 and S2).…”

“…[2] Inspired by the properties of metal enzymes, al arge number of metal complexc atalyzed CÀHo xidations have been explored in the past decades. [3] As ar esult, metal complexes that can mimic the reactivity and selectivity of enzymes have emerged as promising catalysts for alkane oxidation with broad substrate scope. In 1980, Hill and Schardt demonstrated that manganese(III) porphyrin catalyzes the hydroxylation and halogenation of cyclohexane with al arge excess of iodosylbenzene as the oxidant( Scheme 1).…”

Chiral Manganese Aminopyridine Complexes: the Versatile Catalysts of Chemo‐ and Stereoselective Oxidations with H2O2

“…(+)‐Sclareolide was obtained from (‐)‐ambroxide via C−H oxidation with H 2 O 2 , catalyzed by Mn‐dpo . The latter catalyst was also capable of mediating the conversion of simple tetrahydrofuran molecule to γ ‐butyrolactone, the direct precursor of sodium oxibate, used to treat excessive daytime sleepiness …”

Site‐ and Enantioselective C−H Oxygenation Catalyzed by a Chiral Manganese Porphyrin Complex with a Remote Binding Site

“…Along these lines,t here have been numerous efforts to develop enantioselective oxygenation methods in which atransition-metal catalyst mediates the oxygenation of prochiral methylene compounds with as toichiometric oxidant. Common transition metals employed in these catalysts include ruthenium, [2,3] iron, [4,5] and manganese, [6,7] and the chirality is typically provided by ac hiral ligand. Some prominent examples for benzylic oxygenation reactions include the use of ac hiral ruthenium porphyrin complex (up to 76 % ee at 36 %c onversion), ac hiral iron porphyrin complex (up to 72 % ee at 47 %yield based on oxidant), and ac hiral manganese salen complex (up to 87 % ee at 13 % yield).…”