Oxygen Atom Transfer Mechanism for Vanadium‐Oxo Porphyrin Complexes Mediated Aerobic Olefin Epoxidation. Issue 1 (25th November 2021)

• Record Type: Journal Article
• Authors: Liu, Xiao‐Hui; Huang, Jia‐Ying; Tao, Lei‐Ming; Yu, Hai‐Yang; Zhou, Xian‐Tai; Xue, Can; Han, Qi; Zou, Wen; Ji, Hong‐Bing
• Is Part Of: Chinese journal of chemistry. Volume 40:Issue 1(2022)
• Page Start: 115
• Page End: 122
• Publication Date: 2021-11-25
• Subjects: Vanadium‐oxo porphyrin -- Epoxidation -- Reaction mechanisms -- Oxygen atom transfer -- Radicals; Chemistry -- Periodicals; 540.5
• DOI: 10.1002/cjoc.202100576
• Languages: English
• ISSNs: 1001-604X

Abstract

Comprehensive Summary: The development of catalytic aerobic epoxidation by numerous metal complexes in the presence of aldehyde as a sacrificial reductant (Mukaiyama epoxidation) has been reported, however, comprehensive examination of oxygen atom transfer mechanism involving free radical and highly reactive intermediates has yet to be presented. Herein, meso ‐tetrakis(pentafluorophenyl) porphyrinatooxidovanadium(IV) (VOTPFPP) was prepared and proved to be efficient toward aerobic olefin epoxidation in the presence of isobutyraldehyde. In situ electron paramagnetic resonance spectroscopy ( in situ EPR) showed the generation, transfer pathways and ascription of free radicals in the epoxidation. According to the spectral and computational studies, the side‐on vanadium‐peroxo complexes are considered as the active intermediate species in the reaction process. In the cyclohexene epoxidation catalyzed by VOTPFPP, the kinetic isotope effect value of 1.0 was obtained, indicating that epoxidation occurred via oxygen atom transfer mechanism. The mechanism was further elucidated using isotopically labeled dioxygen experiments and density functional theory (DFT) calculations. Abstract : Oxo vanadium porphyrins are proved to be efficient for the aerobic epoxidation of olefins. The exact types of free radicals and their transfer pathways are characterized by operando EPR. VO(O) porphyrin π‐cation radical species from O—O bond homolysis of VO‐acylperoxo species was identified and characterized spectroscopically.