Metal versus Ligand-Centered Oxidizing Equivalents in Hydrocarbon Oxidations

这个无机、生物无机和有机金属化学项目的奖项支持密苏里大学Rolla分校的Pericles Stavropoulos教授开发和机械研究铁基碳氢化合物氧化系统，该系统可以将氧化能力储存在高价金属-氧位点上，但也有可能将氧化等价物作为配体中心自由基离域。为了实现这一目标，合适的配体和铁试剂，在氧供体存在的情况下，应该同时支持一个高价的Fe(IV)=O单元和一个配体中心的p自由基。这些将用于脂肪族和不饱和碳氢化合物的催化氧化，并将收集表明选择性氧化途径的初步机制数据。由金属中心和配体中心氧化等价物的存在所产生的机制含义，与它们在中介碳氢化合物活化过程中的单独作用有关。建议的研究工作集中在三足三胺胺配体上，其富电子特性应有助于稳定高价金属位。这些配体具有邻苯二胺部分，在氧化配体重排后可以保留一个或多个氧化等价物。为了控制生成真正的[LFe(IV)=O]所必需的立体电子参数，将对含有[LFe(II)]和[LFe(III)]的化合物和氧供体分子进行反应性研究，以评估每个配体。最合适的候选物将在烷烃和烯烃的催化氧化中进行测试，通过与涉及不加选择地氧化化学的不良途径进行比较来评估该过程的选择性。以金属为中心的事件将通过表征金属/氧供体相互作用中产生的关键中间体来进行研究。拟议的工作旨在更好地定义获得难以捉摸的Fe(V)=O单元所需的要求及其与为碳氢化合物选择性氧化为商品氧产物制备有用试剂的关系。更广泛的影响超出了对博士后、研究生和本科生研究人员的培训，还包括通过一个移动实验室让农村的K-12学生参与进来，使他们能够动手实验和讨论双氧化学，并为这些群体制作书面材料。

This award in the Inorganic, Bioinorganic and Organometallic Chemistry program supports research by Professor Pericles Stavropoulos at the University of Missouri at Rolla to develop, and mechanistically investigate, iron-based, hydrocarbon-oxidizing systems that can store oxidizing power onto a high-valent metal-oxo site, but also have the potential to delocalize oxidizing equivalents as ligand-centered radicals. To accomplish this, suitable ligands and iron reagents, which, in the presence of oxo donors, should simultaneously support a high-valent Fe(IV)=O unit and a ligand-centered p radical will be synthesized. These will be employed in the catalytic oxygenation of aliphatic and unsaturated hydrocarbons, and initial mechanistic data that indicate selective oxidation pathways will be collected. Mechanistic implications arising from the presence of both metal- and ligand-centered oxidizing equivalents, in relation to their individual roles in mediating hydrocarbon-activation processes will be determined. The proposed research work concentrates on tripodal trisamidoamine ligands, whose electron-rich character should help stabilize high-valent metal sites. These ligands possess o-phenyldiamine moieties, which, can retain one or more oxidizing equivalents following oxidative ligand rearrangement. In an effort to gain control over those stereo-electronic parameters necessary for the generation of an authentic [LoFe(IV)=O] moiety reactivity studies are will be undertaken involving [LFe(II)] and [LFe(III)] containing compounds and oxo-donor molecules to evaluate each ligand. The most suitable candidates will be tested in catalytic oxygenations of alkanes and olefins, to assess the selectivity of the process by comparison to undesirable pathways involving indiscriminate oxygenation chemistry. Metal-centered events will be examined by characterizing key intermediates generated in metal/oxo-donor interactions. The proposed work aims at a better definition of the requirements needed to attain the elusive Fe(V)=O unit and its relation to preparing useful reagents for the selective oxygenation of hydrocarbons to commodity oxo products. Broader impacts extend beyond the training of post-doctoral, graduate, and undergraduate researchers to include involving rural K-12 students through a mobile laboratory that enables hands-on experimentation and discussion of dioxygen chemistry and producing written materials for these groups.