Exploitation of strongly pi-donating Ylidic substituents

用另一个原子或原子团取代一个分子中的一个或多个氢原子（称为取代基），将产生一个相对于母体结构具有改变性质的新分子。取代基的影响可以是非常显著的，并提供了从简单的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，就产生了对空气敏感的乙烯衍生物，可以用作化学合成中的均相还原剂。在另一个例子中，20年前人们发现，用氨基取代基取代亚甲基（母体“卡本”，作为反应中间体的寿命很短）中的氢原子，可以得到可装瓶的固体，这种固体现在在化学的许多领域无处不在。这些，以及许多其他的成就，都是由于氨基取代基极好的“提供pi”效应。然而，最近的结果表明，所谓的“酰基”取代基作为pi给体超越了经典的氨基官能团。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，是拟议研究计划的中心主题。本研究的具体目标包括：1)制备最有效的有机还原剂，作为非均相金属的选择性和均相替代品。没有金属副产物对药物合成具有特别的价值；2)迄今为止难以捉摸的反应中间体的稳定。这些化合物在许多合成途径中被称为瞬时分子，它们的稳定性将提供重要的基础知识，但也允许它们在其他应用中使用（就像碳烯）；3)制备能够向过渡金属提供高于平均水平电子密度的新化合物族（配体）。这些配体随后将用于过渡金属催化，目标是为与天然产物和材料科学相关的新的或改进的合成方法发现高活性催化剂。

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.