Hydrocarbon oxidation with hydrogen peroxide and pentafluoroiodosylbenzene catalyzed by unusually distorted macrocycle manganese complexes

The highly distorted aza macrocycle manganese complexes as the oxidation catalyst were synthesized newly to achieve more green hydrocarbon oxidation; macrocycle 1 ringed by two bipyridine moieties and macrocycle 3 with two bipyridine and two amide bonds in the ring were prepared, and the catalytic abilities of these macrocycle manganese complexes 2 and 4 were examined. A remarkable result is that the unusually distorted manganese complex 4 coordinated by two nitrogen and two oxygen atoms of the macrocyclic ring is capable of catalyzing efficient oxidation of various alkanes and aromatic compounds with hydrogen peroxide. Catalyzed by this complex 4, a variety of alkenes can be oxidized by hydrogen peroxide and their epoxides are formed in high yields. In contrast, complex 2 shows the failure to catalyze efficient oxidation of hydrocarbons with hydrogen peroxide. To evaluate the catalytic abilities of new complexes 2 and 4 strictly, the alkene oxidation was conducted by employing 2 and 4 as the catalyst and pentafluoroiodosylbenzene as the terminal oxidant, and as a result, these complexes 2 and 4 were capable of converting various types of alkenes to their oxidation products with high yields. Moreover, the following new results were found. (A) Norbornene oxidation catalyzed by complexes 2 with different length of side chains indicates that the yield and exo/endo of epoxide depend on the side chains, suggesting that the side chain could control the catalytic ability. (B) The product distribution of styrene oxidation catalyzed by complex 2 differs greatly from that by complex 4, suggesting that the macrocyclic structure and coordinated atom affect the alkene oxidation.

Graphical abstractAn unsymmetrical macrocycle Mn complex with the unusually distorted structure was found to catalyze efficient oxidation of alkanes and aromatic compounds with hydrogen peroxide, and the selective epoxidation of alkenes was also observed. The specific epoxidation of alkenes catalyzed by the strained macrocycle Mn complexes consisting of two bipyridine moieties was found. The mechanism and the relationship between the macrocyclic structure and the oxidation products were discussed. Figure optionsDownload full-size imageDownload as PowerPoint slide