單核錳金屬超氧錯合物：合成、鑑定及其反應性

Mononuclear Manganese(III) Superoxo Complexes: Synthesis, Characterization and Reactivity

林延壕(Lin Yen-Hao)

指導教授 ： 李位仁

國立臺灣師範大學/理學院/化學系/博士(2020年)

https://doi.org/10.6345/NTNU202000745

摘要

相較於含鐵金屬仿生錯合物，以含錳金屬仿生錯合物進行氧氣活化的反應是較少被科學家拿來進行探討。本研究使用三氮二氧配位基 (H2BDPP和H2BDPBrP)。與二價錳金屬離子進行錯合反應，分別形成MnII(BDPP) (1) 和MnII(BDPBrP) (2)。在−80 °C下加入氧氣會分別形成MnIII(BDPP)(O2•) (3) 和MnIII(BDPP)(O2•) (4)，以UV-Vis、rRaman和EPR光譜，可鑑定其為錳超氧錯合物，且其自旋組態為S = 3/2。錯合物3和4也可以與TEMPO-H進行氫原子轉移反應生成MnIII(BDPP)(OOH) (5)和MnIII(BDPBrP)(OOH) (6)，由EPR光譜可以得知其自旋組態為S = 2。除此之外，錯合物 [MnIII(BDPP)(H2O)](OTf) (7)和 [MnIII(BDPP)(H2O)](OTf) (8)加入H2O2/TEA (2:1)也可形成錯合物5和6。錯合物4與2-phenylpropinaldehyde (2-PPA) 進行親核反應，可以生成產物acetophenone。錯合物4在−120 °C與一當量的trifluoroacetic acid (TFA) 反應會形成 [MnIV(BDPBrP)(OOH)]+ (9)，可以UV-Vis、rRaman和EPR光譜鑑定。錯合物9也可以加入一當量的TEA或DBU進行去質子化轉變回錯合物 (4)。由MnIII(BDPBrP)(OOH) (6) 低溫循環伏安法實驗可以得到quasi-reversible的訊號，其還原電位為0.19 V (v.s. Fc/Fc+)，並且可以藉由氧化劑magic blue氧化生成錯合物9，錯合物9也可以藉由還原劑decamethylferrcene還原為錯合物6。由錯合物6的還原電位0.19 V和錯合物9的pKa = 12.5 ~ 11.1求出錯合物6中OO-H的鍵能為85.6 ~ 87.5 kcal/mol。將路易酸的金屬離子Sc(OTf)3和Zn(OTf)2加入錯合物4會進行metal-coupled electron-transfer反應形成 [MnIVBDPBrP(OO)(Sc(OTf)n)](3−n)+ (10) 和[MnIVBDPBrP(OO)(Zn(OTf)n)](2−n)+ (11)。但加入較弱的路易酸金屬離子Ca(OTf)2卻不會進行metal-coupled electron-transfer。藉由以上的探討，可以更進一步的了解三價錳超氧化物的反應特性。

關鍵字

氧氣活化 ； 金屬超氧化合物反應性 ； 三價錳超氧化物 ； 三價錳金屬過氧氫化物 ； 四價錳金屬過氧氫化物

並列摘要

Comparing to biomimetic Fe-containing complexes, the biomimetic Mn-containing complexes invented for dioxygen activation is much less explored. In this study, two ligands, H2BDPP and H2BDPBrP were employed to react with MnII ion for the preparation of MnII(BDPP) (1) and MnII(BDPBrP) (2). Both MnII complexes were reacted with O2 at −80 °C to form MnIII–superoxo intermediates MnIII(BDPP)(O2•) (3) and MnIII(BDPBrP)(O2•) (4) characterized by UV-Vis, rRaman and EPR spectroscopy. The spin state of 3 and 4 was 3/2 with a high-spin MnIII center (SMn = 2) antiferromagnetically coupled with a superoxo radical ligand (SOO• = 1/2). Complexes 3 and 4 could perform hydrogen atom abstraction towards TEMPOH at −90 °C to form MnIII(BDPP)(OOH) (5) and MnIII(BDPBrP)(OOH) (6) characracterized by UV-Vis and EPR spectroscopy. The spin state (S = 2) of 5 and 6 is comfirmed by parallel-mode EPR spectroscopy. Besides, Complexes 5 and 6 can also be synthesized by the reactions of [MnIII(BDPP)(H2O)]OTf (7) and [MnIII(BDPBrP)(H2O)]OTf (8) with H2O2/TEA (2:1). Noteworthily, complex 4 is capable of reacting with 2-PPA at −80 °C to produce acetophenone. Intrestingly, complex 4 treated with trifluoroacetic acid at −120 °C generated [MnIVBDPBrP(OOH)]+ (9), which can be deprotonated by 1 equiv. of TEA or DBU to reproduce complex 4. Also, reaction of 4 reacted with Sc(OTf)3 or Zn(OTf)2 induced metal-coupled electron-transfer to form dinuclear MnIV/ScIII and MnIV/ZnII briged peroxo complexes [MnIVBDPBrP(OO)(Sc(OTf)n)](3−n)+ (10) and [MnIVBDPBrP(OO)(Zn(OTf)n)](2−n)+ (11). However, complex 4 did not react with the weaker Lewis acid Ca(OTf)2. In addition, cyclic votalmetry of MnIII(BDPBrP)(OOH) (6) was performed to obtain E1/2 = 0.19 V (v.s. Fc/Fc+) at −80 °C. From E1/2 of 6 and pKa of 9 (12.5 ~ 11.1), we can estimated the bond dissociation freee energy of the OO-H bond in 6 was around 85.6 ~ 87.5 kcal/mol. In conclusion, these results can in-depth understand the reactivity of MnIII-superoxo complexes.

並列關鍵字

oxygen activation ； metal-superoxo reactivity ； MnIII-superoxo ； MnIII-hydroperoxo ； MnIV-hydroperoxo

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