Lin Yen-Hao, Cramer Hanna Hinrika, van Gastel Maurice, Tsai Yi-Hsuan, Chu Chi-Yi, Kuo Ting-Shen, Lee I-Ren, Ye Shengfa, Bill Eckhard, Lee Way-Zen
Max-Planck-Institut für Chemische Energiekonversion , Mülheim an der Ruhr D-45470 , Germany.
Max-Planck-Institut für Kohlenforschung , Mülheim an der Ruhr D-45470 , Germany.
Inorg Chem. 2019 Aug 5;58(15):9756-9765. doi: 10.1021/acs.inorgchem.9b00767. Epub 2019 Jul 22.
Metal-superoxo species are typically proposed as key intermediates in the catalytic cycle of dioxygen activation by metalloenzymes involving different transition metal cofactors. In this regard, while a series of Fe-, Co-, and Ni-superoxo complexes have been reported to date, well-defined Mn-superoxo complexes remain rather rare. Herein, we report two mononuclear Mn-superoxo species, Mn(BDPP)(O) (, HBDPP = 2,6-bis((2-()-diphenylhydroxylmethyl-1-pyrrolidinyl)methyl)pyridine) and Mn(BDPP)(O) (, HBDPP = 2,6-bis((2-()-di(4-bromo)phenylhydroxyl-methyl-1-pyrrolidinyl)methyl)pyridine), synthesized by bubbling O into solutions of their Mn precursors, Mn(BDPP) () and Mn(BDPP) (), at -80 °C. A combined spectroscopic (resonance Raman and electron paramagnetic resonance (EPR) spectroscopy) and computational study evidence that both complexes contain a high-spin Mn center ( = 2) antiferromagnetically coupled to a superoxo radical ligand ( = 1/2), yielding an overall = 3/2 ground state. Complexes and were shown to be capable of abstracting a H atom from 2,2,6,6-tetramethyl-1-hydroxypiperidine (TEMPO-H) to form Mn-hydroperoxo species, Mn(BDPP)(OOH) () and Mn(BDPP)(OOH) (). Complexes and can be independently prepared by the reactions of the isolated Mn-aqua complexes, [Mn(BDPP)(HO)]OTf () and [Mn(BDPP)(HO)]OTf (), with HO in the presence of NEt. The parallel-mode EPR measurements established a high-spin = 2 ground state for and .
金属超氧物种通常被认为是金属酶催化双氧活化循环中的关键中间体，这些金属酶含有不同的过渡金属辅因子。在这方面，虽然迄今为止已经报道了一系列铁、钴和镍的超氧配合物，但结构明确的锰超氧配合物仍然相当罕见。在此，我们报道了两种单核锰超氧物种，Mn(BDPP)(O)（HBDPP = 2,6 - 双((2 - () - 二苯基羟甲基 - 1 - 吡咯烷基)甲基)吡啶）和Mn(BDPP)(O)（HBDPP = 2,6 - 双((2 - () - 二(4 - 溴苯基)羟甲基 - 1 - 吡咯烷基)甲基)吡啶），它们是通过在 - 80°C下将O₂鼓泡到其锰前体Mn(BDPP)()和Mn(BDPP)()的溶液中合成的。结合光谱学（共振拉曼和电子顺磁共振（EPR）光谱）和计算研究表明，这两种配合物都包含一个高自旋的Mn中心（= 2），通过反铁磁耦合到一个超氧自由基配体（= 1/2），产生一个总自旋为3/2的基态。配合物 和 被证明能够从2,2,6,6 - 四甲基 - 1 - 羟基哌啶（TEMPO - H）中夺取一个H原子，形成锰氢过氧物种，Mn(BDPP)(OOH)()和Mn(BDPP)(OOH)()。配合物 和 可以通过分离的锰水配合物[Mn(BDPP)(H₂O)]OTf()和[Mn(BDPP)(H₂O)]OTf()在NEt存在下与H₂O₂反应独立制备。平行模式的EPR测量确定了 和 的高自旋 = 2基态。
