Department of Chemistry, Seoul National University, 1 Gwanak-ro, Gwanak-gu, Seoul, 08826, Korea.
Department of Fine Chemistry, Seoul National University of Science and Technology, 232 Gongneung-ro, Nowon-gu, Seoul, 01811, Korea.
Chemistry. 2021 Mar 8;27(14):4700-4708. doi: 10.1002/chem.202005183. Epub 2021 Feb 5.
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.
高价金属-氧物种是许多金属酶催化循环中氧原子转移步骤的关键中间体。虽然这些酶的氧化还原活性金属中心通常由阴离子氨基酸侧链或卟啉环支撑，但肽骨架可以作为强电子供体配体来稳定高氧化态。为了在合成环境中检验这一想法的可行性，我们合成了一种新型酰胺型多齿配体的镍(II)配合物。该 N5 配体的单核镍配合物可以在 mCPBA 作为末端氧化剂的条件下催化各种烯烃的环氧化反应。值得注意的是，对于末端烯烃底物，观察到了非常高的催化效率和选择性。我们发现，次级配位球的质子化是催化循环的切入点，其中随后形成高价镍物种以进行氧转移反应。类似的过程可能允许金属酶通过次级配位球中的质子开关来控制初级配位球中的催化循环。
