Merging Bioinorganics and Organometallics: NHC-Ligated Iron-Oxo and Iron-Peroxo Complexes for Catalytic C-H Activation and Functionalization

含铁酶允许生命系统利用氧气选择性氧化有机底物。高价氧化铁以及铁-超氧和-过氧基物种是这些生化转化的关键中间体，但由于这些物种的高反应活性，鉴定和表征这些物种具有挑战性。合成铁配合物作为铁依赖的金属酶活性中心的模型，极大地促进了我们对这些氧化剂的电子结构和反应活性之间的相关性以及酶的催化循环的理解。此外，生物启发的均相铁催化剂有望实现类似于自然蓝图的高效底物转化，最重要的是C-H基团的选择性氧化。该项目旨在通过稳定含有N-杂环卡宾(NHC)供体的大环配体支架中的生物悬浮铁氧基、-过氧基和-超氧基物种来融合生物无机和有机金属化学的概念。以前的研究表明，这些物种赋予反应性氧铁中间体独特的电子结构和性质。在前期工作的基础上，并与研究组内的几个合作伙伴小组密切合作，我们计划揭示一系列由四NHC和NHC/N-供体杂化大环连接的铁氧化剂，特别是氧化铁(IV)物种的氢原子提取和氧原子转移反应的电子结构和反应性之间的相关性。此外，我们将利用基于NHC的配体平台来探索新型氧铁(V)氧化剂的可及性和反应活性，并将为配体支架配备可调节溶解性或锚定在固体载体上的官能团。这有望推动这类独特的有机金属/生物无机铁络合物朝着可用和坚固的催化剂发展，用于氧化C-H官能化。

Iron-containing enzymes allow living systems to use aerial dioxygen for the selective oxidation of organic substrates. High-valent oxoiron as well as iron-superoxo and -peroxo species are the key intermediates in these biochemical transformations, but identification and characterization of these species is challenging due to their high reactivity. Synthetic iron complexes that serve as models for iron dependent metalloenzyme active sites have significantly advanced our understanding of correlations between electronic structures and reactivities of these oxidants, as well as of the enzymes’ catalytic cycles. Furthermore, bioinspired homogeneous iron catalysts promise to achieve efficient substrate conversions akin to those of the natural blueprints, foremost the selective oxygenation of C-H groups.This project aims at the amalgamation of concepts from bioinorganic and organometallic chemistry by stabilizing biorelevant ironoxo, -peroxo and -superoxo species in macrocyclic ligand scaffolds containing N-heterocyclic carbene (NHC) donors, which were previously shown to impart unique electronic structures and properties to reactive oxoiron intermediates. Based on preliminary work and in close collaborations with several partner groups within the Research Group, we plan to unravel correlations between electronic structures and reactivities for the hydrogen atom abstraction and oxygen atom transfer reactivities of a series of iron oxidants, specifically oxoiron(IV) species, ligated by tetra-NHC and NHC/N-donor hybrid macrocycles. Furthermore, we will probe the accessibility and reactivity of novel oxoiron(V) oxidants using the NHC-based ligand platforms, and we will equip the ligand scaffolds with functional groups for tuning solubilities or anchoring on solid supports. This is expected to advance this unique class of hybrid organometallic/bioinorganic iron complexes towards usable and rugged catalysts for oxidative C-H functionalization.