From Generation of Peroxo and High-Valent Diiron Complexes to Enantioselective C-H Oxidation Catalysts

具有非血红素二铁活性中心(NHFe2)的酶能激活生物系统中的氧气，以催化有机底物的各种氧化和/或氧化反应，这在合成应用中也是有趣的和有前途的。一种这样的反应是未被激活的有机分子的选择性C-H羟基化，包括甲烷单加氧酶(SMMO)使用的最不活跃的底物CH4。NHFe2的催化循环通常采用与氧气反应生成过氧二铁中间体的二亚铁形式。活性物种应该是这种过氧二铁物种或从它衍生出来的物种。在sMMO中，过氧基中间体P转化为高价Fe(IV)Fe(IV)活性物种Q。尽管世界各国都在努力为这种反应获得功能生物启发的二铁模型，但实际催化性能并不足以应用。到目前为止，使用的大多数配体系统主要由含氮的供体组成。然而，在sMMO中有一个富含羧酸的配位环境，这也是许多其他双铁酶的特征。这意味着，这些在结构上非常相似的双铁活性部位的反应性强烈地依赖于末端供体。在这方面，我们想要建立一个具有不同末端给体的双核配体的双铁络合物家族，包括吡啶、咪唑、酚酸盐和羧酸盐以及各种混合形式，以研究它们建立过氧基和/或高价双铁物种的反应性。除了阐明这些过氧基和/或高价物种的分子结构和电子结构外，我们还将研究它们在选定底物羟化反应中的反应活性。由于人们认为分子结构和电子结构决定了反应的活性，我们打算获得分子结构和电子结构与它们的反应性之间的关联，以便我们能够确定选择性C-H氧化的最佳催化体系。为此，我们将合成具有不同末端给体的双核配体家族的新的衍生物，我们将合成它们的双铁配合物，我们将试图获得高价和过氧基物种，我们将研究它们的活性和催化性能。然而，我们不想停留在传统的C-H活化底物环己烷上，但我们也想在这种C-H键活化中引入对映选择性。因此，我们将尝试在去核配体体系中引入手性，以获得用于精选底物的手性C-H活化的手性催化剂。

Enzymes with a non-heme diiron active site (NHFe2) activate dioxygen in biological systems to catalyze a variety of oxidation and/or oxygenation reactions of organic substrates, that are also interesting and promising for synthetic applications. One such reactivity is the selective C-H hydroxylation of not activated organic molecules including the least reactive substrate CH4 used by methane monooxygenase (sMMO). The catalytic cycles of NHFe2 generally employ a diferrous form that reacts with dioxygen to a peroxo-diferric intermediate. The active species is supposed to be either this peroxo-diferric species or a species derived from it. In sMMO, the peroxo intermediate, P, converts to a high-valent Fe(IV)Fe(IV) active species, Q. Despite strong worldwide efforts to obtain functional bioinspired diiron models for this reactivity, the actual catalytic performances are not good enough for application. Most ligand systems used so far are mainly comprised of nitrogen-containing donors. However, in sMMO there is a carboxylate-rich coordination environment, that is also characteristic for many other diiron enzymes. This implies, that the reactivity of these otherwise structurally very similar diiron active sites depends strongly on the terminal donors. In this respect, we want to establish a family of diiron complexes with dinucleating ligands that vary in their terminal donors including pyridine, imidazole, phenolate, and carboxylate and all kind of mixed forms to study their reactivity for building peroxo and/or high-valent diiron species. Besides the elucidation of the molecular and electronic structures of these peroxo and/or high-valent species, we will investigate their reactivities in the hydroxylation of selected substrates. As it is thought that the molecular and electronic structure dictate reactivity, we intend to obtain correlations between the molecular and electronic structures with their reactivities so that we can identify the best catalytic systems for selective C-H oxidations. For this, we will synthesize new derivatives of our family of dinucleating ligands with different terminal donors, we will synthesize their diiron complexes, we will try to obtain high-valent and peroxo species, and we will study their reactivites and catalytic abilities. However, we don’t want to stay with traditional substrates for C-H activation as cyclohexane, but we also want to introduce an enantioselectivity to this C-H bond activation. Therefore, we will try to introduce chirality into the dinucleating ligand system so that we can obtain chiral catalysts for the enantioselective C-H activation of carefully chosen substrates.