以新穎配位基合成錳-氧加成物及其對9,10-Dihydroanthracene的催化探討

Abstract

在許多含錳酵素催化循環的研究中，錳氧錯合物與錳過氧氫化物被認為是可能存在的中間體，尤其在第二光系統(Photosystem II)中的氧釋放複合體(Oxygen-Evolving Complex)、含錳雙加氧酶(Manganese-Dependent Dioxygenase)和草酸脫羧酶(Oxalate Decarboxylase)。為了證實這些中間體的存在並探討其特質，本研究利用新穎配位基(H2BDBP)合成錳錯合物MnII(BDBP)(NaOTf) (1)，並讓其與氧氣在低溫下反應生成Mn(BDBP)(O2) (4)。透過循環伏安法、低溫UV光譜和EPR光譜鑑定此催化反應之中間產物，並與過去合成的錳錯合物MnII(BDPP)及MnII(BDPBrP)進行光學性質及結構上的比較，以解析Mn(BDBP)(O2) (4)錳金屬中心價數。除了新穎錳團簇物之結構解析，本研究更探討錯合物針對氫原子轉移反應之催化性。我們分別以HOTf、TEMPOH、9,10-Dihydroanthracene(簡稱DHA)等物質的做為受質，發現以下新穎化學反應性: Mn(BDBP)(O2) (4)與HOTf在低溫下反應會生成有一個不穩定的中間體，使用EPR光譜判斷為與錯合物 (4)同為高自旋四價錳錯合物(S = 3/2)；而Mn(BDBP)(O2) (4)與TEMPOH進行氫原子轉移反應生成MnIII(BDBP)(OOH) (5) ，透過UV-vis和EPR光譜來鑑定為高自旋三價錳錯合物(S = 2)；使用錯合物 (4)與DHA進行反應時，亦發現其進行了原先MnIII(BDPP)(O2•)和MnIII(BDPBrP)(O2•)無法對DHA進行的氫原子轉移反應並生成蒽(anthracene)。藉由本論文探討，我們可以得知新一代配位基可合成新穎錳錯合物，且該錯合物具有成為新一代氫轉移反應催化劑之潛力，可應用於有機分子的改質反應。

In many catalytic studies of manganese containing enzymes, manganese-dioxygen and -hydroperoxo species are proposed intermediates in their catalytic cycles, specifically for Oxygen-Evolving Complex in Photosystem II, Manganese-Dependent Dioxygenase, and Oxalate Decarboxylase. In order to examine the existence and reactivity of these intermediates, a novel ligand H2BDBP was employed to synthesize a manganese complex, MnII(BDBP)(NaOTf) (1), witch was further reacted with O2 to generate a manganese dioxygen adduct, Mn(BDBP)(O2) (4), at low temperature. In this project topic, we measure the significant electronic state difference of central manganese between Mn(BDBP)(O2) and previous synthesized MnII(BDPP), MnII(BDPBrP) via cyclic voltammetry, cryogenic UV-vis absorption spectroscopy and EPR spectroscopy. Furthermore, reacted with TEMPOH and DHA to reveal its reactivity of complex (4) was towards the hydrogen atom transfer reaction. In addition, complex (4) was also reacted with HOTF at low temperature to produce an metastable intermediate, which is revealed to be a high-spin quatervalent manganese complex as complex (4) via EPR study (S = 3/2). Reaction of complex (4) with TEMPOH resulted in the generation of MnIII(BDBP)(OOH) (5) which is further identified as a high-spin quatervalent manganese complex by UV-vis and EPR spectroscopy (S = 2). Also, we have found that complex (4) will perform the hydrogen atom transfer reaction of DHA to produce anthracene, witch could not be triggered by manganese complexes, MnIII(BDPP)(O2•) and MnIII(BDPBrP)(O2•), synthesized before. These findings show that complex (4) coordinated by the new ligands, BDBP2−, has the potential to be a hydrogen transfer reaction catalyst, which can be applied to organic molecular modification reactions.