|author||Suk Joong Lee|
|journal||Chem. Eur. J. 2017, 23, 11969 – 11976(DOI: 10.1002/chem.201702750)|
A new nickel(II) porphyrin complex, [Ni(porp)] (), has been synthesized and characterized by H NMR, C NMR and mass spectrometry analysis. This Ni porphyrin complex quantitatively catalyzed the epoxidation reaction of a wide range of olefins with meta-chloroperoxybenzoic acid (m-CPBA) under mild conditions. Reactivity and Hammett studies, HO-exchange experiments, and the use of PPAA (peroxyphenylacetic acid) as a mechanistic probe suggested that participation of multiple active oxidants Ni−OOC(O)R , Ni-Oxo , and Ni-Oxo within olefin epoxidation reactions by the nickel porphyrin complex is markedly affected by solvent polarity, concentration, and type of substrate. In aprotic solvent systems, such as toluene, CHCl, and CHCN, multiple oxidants, Ni−(O)R , Ni-Oxo , and Ni-Oxo , operate simultaneously as the key active intermediates responsible for epoxidation reactions of easy-to-oxidize substrate cyclohexene, whereas Ni-Oxo and Ni-Oxo species become the common reactive oxidant for the difficult-to-oxidize substrate 1-octene. In a protic solvent system, a mixture of CHCN and HO (95:5), the Ni−OOC(O)R undergoes heterolytic or homolytic O−O bond cleavage to afford Ni-Oxo and Ni-Oxo species by general acid catalysis prior to direct interaction between and olefin, regardless of the type of substrate. In this case, only Ni-Oxo and Ni-Oxo species were the common reactive oxidant responsible for olefin epoxidation reactions.
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