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

具有非血红素双铁活性位点（NHFe2）的酶激活生物系统中的双氧，催化有机底物的各种氧化和/或氧合反应，这也是合成应用中有趣和有前景的。其中一种反应性是对非活化有机分子的选择性C-H羟基化，包括甲烷单加氧酶（sMMO）使用的活性最低的底物CH4。NHFe2的催化循环通常采用二亚铁形式，与二氧反应生成过氧二亚铁中间体。活性物质要么是这个过氧异铁质要么是由它衍生出来的物质。在sMMO中，过氧化物中间体P转化为高价Fe(IV)Fe（IV）活性物质Q.尽管世界范围内都在努力获得这种反应活性的功能性生物激发双铁模型，但实际的催化性能还不够好，无法应用。目前使用的大多数配体系统主要由含氮供体组成。然而，在sMMO中有一个富含羧酸的配位环境，这也是许多其他二铁酶的特征。这表明，这些结构上非常相似的二铁活性位点的反应性在很大程度上取决于末端给体。在这方面，我们想建立一个双核配体家族，其末端供体不同，包括吡啶、咪唑、酚酸盐和羧酸盐以及各种混合形式，以研究它们对构建过氧和/或高价双铁的反应性。除了阐明这些过氧和/或高价物质的分子和电子结构外，我们还将研究它们在选定底物的羟基化反应中的活性。由于认为分子和电子结构决定了反应活性，我们打算获得分子和电子结构与其反应活性之间的相关性，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二核配体家族的新衍生物，我们将合成它们的双铁配合物，我们将尝试获得高价和过氧物质，我们将研究它们的反应活性和催化能力。然而，我们不想继续用环己烷这样的传统底物来激活碳氢键，但我们也想引入对映选择性来激活碳氢键。因此，我们将尝试在二核配体体系中引入手性，这样我们就可以获得手性催化剂，用于精心挑选的底物的对映选择性C-H活化。

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.