Synthesis, Characterization, and Catalytic Activities of A Nickel(II) Monoamido‐Tetradentate Complex: Evidence For Ni<sup>III</sup>–Oxo and Ni<sup>IV</sup>–Oxo Species

et al. 2017

Chemistry A European J

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A new nickel(II) porphyrin complex, [Ni (porp)] (1), has been synthesized and characterized by H NMR, C NMR and mass spectrometry analysis. This Ni 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 O-exchange experiments, and the use of PPAA (peroxyphenylacetic acid) as a mechanistic probe suggested that participation of multiple active oxidants Ni -OOC(O)R 2, Ni -Oxo 3, and Ni -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 Cl , and CH CN, multiple oxidants, Ni -(O)R 2, Ni -Oxo 3, and Ni -Oxo 4, operate simultaneously as the key active intermediates responsible for epoxidation reactions of easy-to-oxidize substrate cyclohexene, whereas Ni -Oxo 3 and Ni -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 CN and H O (95:5), the Ni -OOC(O)R 2 undergoes heterolytic or homolytic O-O bond cleavage to afford Ni -Oxo 3 and Ni -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 -Oxo 3 and Ni -Oxo 4 species were the common reactive oxidant responsible for olefin epoxidation reactions.

Section: Resultsmentioning

confidence: 60%

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

Ahn

Bae

et al. 2017

Chemistry A European J

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“…We found that 1 epoxidized them in moderate yields (47–51 %). Previously reported non‐heme nickel complexes and porphyrin nickel complexes typically show low catalytic activity towards terminal olefins [12c,j] …”

Section: Resultsmentioning

confidence: 99%

“…The selectivity showed a gradual decrease with increasing chain length. No nickel‐based catalysts are currently known that effect catalytic epoxidation of terminal olefins with such high efficiency and selectivity [12c,j] …”

Section: Resultsmentioning

confidence: 99%

“…200 s (Figure 6 a and Figure S10). The X‐band EPR spectrum of 1 is featureless (Figure S11), but an axial signal with g ⊥ = 2.17 and g ∥ = 2.25 developed upon treatment with 1 equiv of mCPBA (Figure S12), which is characteristic of nickel(III) species with low‐spin d 7 ( S = 1/2) electronic configuration [12f,j, 13a, 22] …”

Section: Resultsmentioning

confidence: 99%

“…As synthetic systems inspired by metalloenzymes, nickel‐based catalysts can carry out hydroxylation of alkanes and epoxidation of alkenes using H 2 O 2 , mCPBA, or NaOCl as terminal oxidant [12] . To accommodate high‐valent nickel‐oxo species as active oxidants in the catalytic cycle, various nickel complexes have been developed that are supported by electron‐rich ligands having anionic amidate or neutral guanidyl motif [12f–k] . Only a few nickel‐based catalytic systems, however, are currently available for efficient epoxidation of terminal olefins with high selectivity under mild conditions [13]…”

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Proton Switch in the Secondary Coordination Sphere to Control Catalytic Events at the Metal Center: Biomimetic Oxo Transfer Chemistry of Nickel Amidate Complex

Jeong

et al. 2021

Chemistry A European J

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High‐valent metal‐oxo species are key intermediates for the oxygen atom transfer step in the catalytic cycles of many metalloenzymes. While the redox‐active metal centers of such enzymes are typically supported by anionic amino acid side chains or porphyrin rings, peptide backbones might function as strong electron‐donating ligands to stabilize high oxidation states. To test the feasibility of this idea in synthetic settings, we have prepared a nickel(II) complex of new amido multidentate ligand. The mononuclear nickel complex of this N5 ligand catalyzes epoxidation reactions of a wide range of olefins by using mCPBA as a terminal oxidant. Notably, a remarkably high catalytic efficiency and selectivity were observed for terminal olefin substrates. We found that protonation of the secondary coordination sphere serves as the entry point to the catalytic cycle, in which high‐valent nickel species is subsequently formed to carry out oxo‐transfer reactions. A conceptually parallel process might allow metalloenzymes to control the catalytic cycle in the primary coordination sphere by using proton switch in the secondary coordination sphere.

Bulletin Korean Chem Soc

Electronic properties and reactivity patterns of high‐valent metal‐oxo species of Mn, Fe, Co, and Ni

Li¹,

Cho

Nam

2021

Density functional theory (DFT) calculations were performed for a series of significant terminal high‐valent metal‐oxo complexes, where the metals are Mn, Fe, Co, and Ni, to reveal their electronic property and reactivity patterns toward the inert CH bond activation. We found that as the metal center changes from Mn to Ni, the bond strength of metal‐oxo decreases while the oxyl character of the oxygen increases, which suggests an increase in the hydrogen‐abstraction reactivity. This prediction was further strengthened by theoretical reactivity studies, that is, the reactivities of these four metal‐oxo species toward inert CH bond followed an order of MnO ≈ FeO ≪ CoO < NiO. At the orbital level, it was found that three different electron transfer mechanisms were active among these four species. Thus, this study would provide an explanation and intuitive clues for chemists to understand the nature of the high‐valent late transition metal‐oxo species.