Crystallographic characterization of a synthetic 1:1 end-on copper dioxygen adduct complex
Crystallographic characterization of a synthetic 1:1 end-on copper dioxygen adduct complex
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DOI：
10.1002/anie.200600351
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发表时间：
2006-01-01
影响因子：
16.6
通讯作者：
Schindler, Siegfried
中科院分区：
文献类型：
--
作者：
Wuertele, Christian;Gaoutchenova, Ekaterina;Schindler, Siegfried
合成的生物无机铜分子氧配合物由于其在生物化学和催化中作为氧化剂的突出作用，在过去的几十年里引起了人们极大的兴趣。该领域的最新进展形成了将已知复合物的显著结构多样性与作为氧化剂的反应性差异相关联的基础。[1-3]这些研究中的许多都涉及到微调配体的性质，以稳定各种铜氧化合物，这些化合物在反应性物种的形成中作为中间体出现，并且在很大程度上负责氧化活性。[2，3]从这些研究中产生的集体图像可以在氧与铜络合物结合的一般机制框架内进行讨论（方案1，电荷被省略）[1-4]，类似于最近提出的铁络合物方案。[5]虽然存在关于2：1 Cu/O2物质的配位化学和反应性的大量文献，[2，3，6，7]但1：1 Cu/O2络合物的表征由于这些物质在溶液中二聚或在不可逆配体氧化后分解的固有趋势而变得复杂。因此，到目前为止，仅存在三个1：1 Cu/O2络合物的晶体学表征的实例，它们都表现出侧面（η2）配位模式。[8-12]末端铜二氧加合物已被提出作为单核铜酶催化循环的活性中间体，如肽基甘氨酸α-羟基化单加氧酶（PHM）或多巴胺β-单加氧酶（DβH）。[2，3]事实上，最近这种物种的存在可以通过预催化PHM复合物的X射线晶体学来证明。[13]然而，在生物无机体系中，所有试图分离和表征方案1中第一步的合成类似物的尝试，即形成末端1：1个Cu/O2复合体，至今未能确定年代。（三（2-氨基乙基）胺）或TMPA（三[（2-吡啶基）甲基]胺）配体，这样的配合物是短寿命的，并且只能在低温下使用停流UV/维斯光谱法作为瞬态物质检测。[1-3然而，在相关研究中，我们表明，瞬时物质的高反应性可以通过使用具有更强N-供体特征的空间上更苛刻的配体（例如Me 6 tren）来缓和。[15]这一成功使我们采用空间拥挤的超碱性[17] tren衍生物三（四甲基胍基）tren（TMG 3 tren）[18]作为配体，并且在最近的研究中，我们最终能够在低温下获得稳定的1：1 Cu/O2加合物（方案2）。[19]最合理的是，与以前用其他tren衍生物进行的实验形成鲜明对比，在加热时只观察到不可逆的氧化反应，我们发现Cu-O2加合物的形成是
Synthetic bioinorganic copper dioxygen complexes have attracted great interest in the past decades because of their prominent role as oxidants in biochemistry and catalysis. Recent advances in this field form a basis to correlate the pronounced structural diversity of known complexes with the resulting differences in reactivity as oxidants.[1–3] Many of these studies have been concerned with the fine tuning of ligand properties to stabilize the various copper oxygen compounds that occur as intermediates in the formation of reactive species and which are largely responsible for the oxidation activity.[2, 3] The collective picture arising from these studies can be discussed within a general mechanistic framework of oxygen binding to copper complexes (Scheme1, charges are omitted)[1–4] analogous to a scheme recently proposed for iron complexes.[5] While ample literature exists on the coordination chemistry and reactivity of 2: 1 Cu/O2 species,[2, 3, 6, 7] the characterization of 1: 1 Cu/O2 complexes is complicated by the intrinsic tendency of these species to dimerize in solution or to decompose after irreversible ligand oxidation. Accordingly, to date only three crystallographically characterized examples for 1: 1 Cu/O2 complexes exist, all exhibiting a side-on (η2) coordination mode.[8–12] End-on copper dioxygen adduct complexes have been proposed as reactive intermediates in the catalytic cycle of mononuclear copper enzymes, such as peptidylglycine α-hydroxylating monooxygenase (PHM) or dopamine β-monooxygenase (DβH).[2, 3] And indeed, very recently the existence of such a species could be demonstrated by X-ray crystallography for a precatalytic PHM complex.[13] Yet, in the bioinorganic regime all attempts to isolate and characterize a synthetic analogue of the first step in Scheme 1, that is, the formation of an end-on 1: 1 Cu/O2 complex, failed to date.With tripodal tetradentate tren (tris (2-aminoethyl) amine) or tmpa (tris [(2-pyridyl) methyl] amine) ligands, such complexes are short-lived and could only be detected as transient species at low temperatures using stopped-flow UV/Vis spectroscopy.[1–3, 14–16] In related studies we showed, however, that the high reactivity of the transient species can be moderated by use of sterically more demanding ligands with stronger N-donor character, such as Me6tren.[15] This success led us to employ the sterically congested superbasic [17] tren derivative tris (tetramethylguanidino) tren (TMG3tren)[18] as a ligand and in a recent study we were eventually able to obtain a stable 1: 1 Cu/O2 adduct at low temperatures (Scheme 2).[19] Most remarkably—and in striking contrast to former experiments with other tren derivatives, for which only irreversible oxidation reactions were observed upon warming—we found that the formation of the Cu–O2 adduct is