High-valent metal oxo species stabilized by polyoxovanadates: synthesis, properties and catalytic activity

高价金属氧物种被认为是各种工业和生物催化过程中的关键中间体。本项目研究了新型分子氧化钒簇合物中高价金属氧和金属羟基物种的形成、反应活性和可能的稳定性。金属功能化钒氧化物[M(L)V12O32X]n-(={MV12}，M=过渡金属，L=末端配体，X=卤化物-模板)具有预先形成的金属结合位，由于其氧化催化活性已被证明是高价金属物种生成和稳定的合适模型。特别是，该项目侧重于具有多个可访问的氧化还原转变(FeII、MnII、CoII)的氧化还原活性3D过渡金属，作为工业催化剂(例如Haber-Bosch工艺)以及酶(例如细胞色素P450)的潜在相关模型。此外，选择的4d/5d金属(RuII，IrII)也被采用，因为它们可以促进高价氧配合物的分离和结构表征。金属中心在{MV12}中的结合方式与典型的金属氧基配体(通常是具有三角配位几何构型的氮给电子体)有根本的不同，因此可以预期具有以前未被探索的配位行为和新的反应活性的新的中间体。在第一步中，研究了现有的{MV12}络合物与过氧物和叠氮化物等反应性配体反应形成高价物种以及还原的{MV12}物种对分子氧的活化。利用实验和理论方法对高价中间体进行了表征，以了解它们的电子结构、结合方式和反应活性。只要有可能，使用单晶X射线衍射的结构表征将提供对结合情况的详细了解。高价物种的反应性以及它们作为催化剂的可能用途将通过合成重要的底物氧化来探索，例如环氧化、C-H活化和羟化。原位稳定性研究将提供对可能的团簇重排或胶体形成的洞察。因此，该项目提供了一种全新的化合物类别，其反应性可以根据形成的中间体进行合理化，并且可以通过对存在的金属中心进行化学修饰来调节其反应性。

High-valent metal oxo species are considered key intermediates in various industrial and biological catalytic processes. This project investigates the formation, reactivity and possible stabilization of high-valent metal oxo and metal-hydroxo species in novel molecular vanadium oxide clusters. Metal-functionalized vanadium oxides [M(L)V12O32X]n- (= {MV12}, M = transition metal, L = terminal ligand, X = halide-template) with a pre-formed metal binding site are used as suitable models for the generation and possible stabilization of high-valent metal species as their oxidative-catalytic activity has been shown previously. In particular, this project is focused on redox-active 3d-transition metals with multiple accessible redox-transitions (FeII, MnII, CoII) as potentially relevant models for industrial catalysts (e.g. Haber-Bosch process) as well as enzymes (e.g. cytochrome P450). In addition, selected 4d/5d metals (RuII, IrII) are employed as they can facilitate the isolation and structural characterization of high-valent oxo complexes. The binding mode of metal centres in {MV12} is fundamentally different to typical metal oxo ligands (often: nitrogen donors with trigonal coordination geometry), therefore new intermediates with a previously un-explored coordination behaviour and new reactivity can be expected. In the first step, the formation of high-valent species by reaction of existing {MV12} complexes with reactive ligands such as peroxides and azides as well as the activation of molecular oxygen by reduced {MV12} species is investigated. High-valent intermediates are characterized using experimental and theoretical methods to understand their electronic structure, binding modes and reactivity. Whenever possible, structural characterization using single-crystal X-ray diffraction will provide detailed insight into the binding situation. The reactivity of the high-valent species as well as their possible use as catalysts will be explored using synthetically important substrate oxidations, e.g. epoxidations, C-H-activations and hydroxylations. In situ stability studies will provide insight into possible cluster rearrangement or colloid formation. The project therefore provides access to a completely new compound class whose reactivity can be rationalized based on the intermediates formed and where reactivity can be tuned by chemical modification of the metal centres present.