Exploitation of strongly pi-donating Ylidic substituents

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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.