Synthesis of Metal Xanthene‐Bridged Bis‐corroles and their Catalytic Activity in Aerobic Baeyer‐Villiger Oxidation Reaction

Abstract

The metal (M=Co, Cu, Mn, Sn, Fe) xanthene-bridged bis-corroles (M 2 XBC) were synthesized and used for catalyzing aerobic Baeyer-Villiger (B-V) oxidation of cyclic ketones to corresponding lactones. It turns out iron (IV) bis-corrole complex (Fe 2 XBC) exhibited excellent activity and selectivity towards the B-V oxidation of various cyclic ketones at very low catalyst loading. The yield of ɛ-caprolactone could reach 98% with only 0.005 mol% catalyst. The turnover number (TON) of the Fe 2 XBC catalyst could even be up to 17400 in a gram-scale oxidation of cyclohexanone, showing the promising for industrial usage. Moreover, the existences of benzoyl radical and benzoylperoxy radical in the reaction were proved by ESI-HRMS spectra and electron paramagnetic resonance (EPR) spectra. A plausible radical mechanism for the metal bis-corrole catalyzed aerobic B-V oxidation of cyclohexanone in the presence benzaldehyde additive was proposed.

Enhanced Photoinduced Baeyer–Villiger Oxidation of Ketones by Introducing Trinuclear Ruthenium Clusters into Polyoxometalate-Based Metal–Organic Frameworks

“…The reaction yields decreased to 14.1% and <1 in the absence of O 2 or benzaldehyde, respectively (Table , entries 8 and 9), suggesting both O 2 and benzaldehyde are involved in the photocatalytic oxidation process. Furthermore, only trace target products were detected after the incorporation of the radical scavenger 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) equivalent to benzaldehyde in the reaction system (Table , entry 10), implying that the photocatalytic reaction involves the free radical pathway. , These controlled experiments would help us to infer the reaction mechanism.…”

“…The catalytic activity of CR-SiW 12 (catalyst dosage of 0.1 mol %, reaction time of 3 h, yield of 94.1%) was much higher than that of AcrH + ClO 4 – (catalyst dosage of 5 mol %, reaction time of 20 h, yield of 92%). Besides, compared with the conventional thermal-driven B–V oxidation of cyclohexanone (high temperature and pressure), our scheme has the advantages of mild reaction conditions, utilization of clean solar energy, high catalytic efficiency, and reusability, effectively reducing energy consumption, and avoiding the use of high-risk production equipment and other potential risks. − …”

“…The other one is a set of higher triplet peaks (•), which are characteristic signal peaks of the benzoyl peroxy radical (C 6 H 5 COOO • ) adduct of PBN. 5,6,11 As elucidated by EPR results, CR-SiW 70 Finally, perbenzoic acid and cyclohexanone result in the formation of Criegee adduct intermediates, which undergo an intramolecular rearrangement to produce ε-caprolactone and benzoic acid. 7,9,13,67 ■…”

“…In particular, the O 2 /aldehyde system known as the Mukaiyama method is very attractive in industrial production owing to its advantages of safety, green nonpollution, and high yield. , Recently, researchers have reported a lot of excellent work to develop a low-cost B–V oxidation process based on the Mukaiyama method. Nevertheless, conventional thermo-catalytic technologies often require high-temperature energy to trigger the catalytic reaction, which still suffers from the issues of high energy consumption and advanced facility requirements, thereby limiting the scalability of the process. − Recent studies show that photocatalytic technology has become a research hotspot in the field of organic synthesis by utilizing economical solar energy as the driving force, with advantages including mild reaction conditions, high selectivity, and environmental friendliness. − Consequently, the development of the photoinduced B–V oxidation process based on the Mukaiyama method is of great research significance.…”

“…Furthermore, only trace target products were detected after the incorporation of the radical scavenger 2,2,6,6-tetramethylpiperidine-1oxyl (TEMPO) equivalent to benzaldehyde in the reaction system (Table 1, entry 10), implying that the photocatalytic reaction involves the free radical pathway. 5,6 These controlled experiments would help us to infer the reaction mechanism. We fully ground the CR-SiW 12 crystals prior to the catalytic experiments.…”