Synthesis, Characterization, and Efficient Catalytic Activities of a Nickel(II) Porphyrin: Remarkable Solvent and Substrate Effects on Participation of Multiple Active Oxidants

A new nickel(II) porphyrin complex, [Ni II (porp)] ( 1 ), has been synthesized and characterized by 1 H NMR, 13 C NMR and mass spectrometry analysis. This Ni II porphyrin complex  1 quantitatively catalyzed the epoxidation reaction of a wide range of olefins with meta ‐chloroperoxybenzoic acid ( m ‐CPBA) under mild conditions. Reactivity and Hammett studies, H 2 18 O‐exchange experiments, and the use of PPAA (peroxyphenylacetic acid) as a mechanistic probe suggested that participation of multiple active oxidants Ni II −OOC(O)R 2 , Ni IV ‐Oxo 3 , and Ni III ‐Oxo 4 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, CH 2 Cl 2 , and CH 3 CN, multiple oxidants, Ni II −(O)R 2 , Ni IV ‐Oxo 3 , and Ni III ‐Oxo 4 , operate simultaneously as the key active intermediates responsible for epoxidation reactions of easy‐to‐oxidize substrate cyclohexene, whereas Ni IV ‐Oxo 3 and Ni III ‐Oxo 4 species become the common reactive oxidant for the difficult‐to‐oxidize substrate 1‐octene. In a protic solvent system, a mixture of CH 3 CN and H 2 O (95:5), the Ni II −OOC(O)R 2 undergoes heterolytic or homolytic O−O bond cleavage to afford Ni IV ‐Oxo 3 and Ni III ‐Oxo 4 species by general acid catalysis prior to direct interaction between 2 and olefin, regardless of the type of substrate. In this case, only Ni IV ‐Oxo 3 and Ni III ‐Oxo 4 species were the common reactive oxidant responsible for olefin epoxidation reactions.