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使用空气中的分子氧来选择性氧化有机底物。高价氧代铁以及铁-superoxo和-peroxo物种是这些生化转化的关键中间体，但这些物种的鉴定和表征是具有挑战性的，由于它们的高反应性。合成的铁配合物作为铁依赖性金属酶活性位点的模型，大大提高了我们对这些氧化剂的电子结构和反应性之间的相关性，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天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相关铁氧，-过氧和-超氧物种，其先前显示赋予反应性氧代铁中间体独特的电子结构和性质。基于初步工作，并与研究小组内的几个合作伙伴小组密切合作，我们计划解开电子结构和反应性之间的相关性的氢原子提取和氧原子转移反应性的一系列铁氧化剂，特别是氧合铁（IV）物种，连接四-NHC和NHC/N-供体混合大环。此外，我们将使用基于NHC的配体平台探测新型氧代铁（V）氧化剂的可及性和反应性，并且我们将为配体支架配备用于调节溶解度或锚定在固体支持物上的官能团。这有望将这类独特的混合有机金属/生物无机铁络合物推向用于氧化C-H官能化的可用且坚固的催化剂。

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.