Exploitation of strongly pi-donating Ylidic substituents

用另一个原子或原子团（称为取代基）取代分子中的一个或多个氢原子，将导致新分子相对于母体结构具有改变的性质。取代基的影响可能非常显著，并提供了从简单框架获得重要化学性质的机会。例如，用四个氮基取代基（氨基）取代惰性气体分子乙烯中的四个氢原子，产生一种空气敏感的乙烯衍生物，可用作化学合成中的均相还原剂。在另一种情况下，二十年前发现，用氨基取代基取代亚甲基（母体“卡宾”作为反应性中间体的寿命很短）中的氢原子会导致可装瓶的（！）现在在化学的许多领域中已经变得普遍存在的固体。这些和许多其他成就，是由于氨基取代基的极好的“π-供体”效应。然而，最近的结果表明，所谓的“ylidic”取代基超过经典的氨基功能作为π-供体。有针对性地利用这一事实将开辟基础化学和应用化学的许多新途径，是拟议的研究计划的中心主题。本研究的具体目标包括：1）制备最强大的有机还原剂，作为多相金属的选择性和均相替代品。不存在金属副产物对于药物合成具有特别的价值; 2）稳定迄今为止难以捉摸的反应性中间体。这些化合物在许多合成途径中被用作瞬态分子，它们的稳定化将提供重要的基础知识，但也允许它们用于其他应用（正如卡宾）; 3）制备能够向过渡金属提供高于平均水平的电子密度的新化合物家族（配体）。这些配体随后将用于过渡金属催化，目标是发现用于与天然产物和材料科学相关的新的或改进的合成方法的高活性催化剂。

Replacing one or more hydrogen atoms in a molecule by another atom or group of atoms, known as a substituent, will result in a new molecule with altered properties relative to the parent structure. The influence of the substituent can be very dramatic and offers the opportunity to access important chemical properties from even simple frameworks. As an example, the substitution of the four hydrogen atoms in ethene, an inert gaseous molecule, with four nitrogen-based substituents (amino groups) gives rise to an air-sensitive ethene derivative that can be used as a homogeneous reducing agent in chemical synthesis. In another case, it was discovered two decades ago that replacing hydrogen atoms in methylene (the parent "carbene" with a fleeting lifetime as a reactive intermediate) with amino substituents leads to bottle-able(!) solids that have now become ubiquitous in many areas of chemistry. These, and many other achievements, result from the superb "pi-donating" effects of the amino substituents. Recent results, however, have demonstrated that so-called "ylidic" substituents surpass classical amino functionalities as pi-donors. The targeted exploitation of this fact will open up many new avenues of fundamental and applied chemistry, and is the central theme of the proposed research program. Specific goals of this research include: 1) the preparation of the most powerful organic reducing agents as selective and homogeneous alternatives to heterogeneous metals. The absence of metallic by-products is of particular value for pharmaceutical syntheses; 2) the stabilization of as-of-yet elusive reactive intermediates. These compounds are invoked as transient molecules in many synthetic pathways and their stabilization will provide important fundamental knowledge, but also allow for them to be used in other applications (just as for carbenes); 3) the preparation of new families of compounds (ligands) capable of donating above-average amounts of electron density to transition metals. These ligands will subsequently be used in transition metal catalysis, with the goal of discovering highly active catalysts for new or improved synthetic methodologies relevant to natural products, and materials science.