Development of Concepts for the Efficient Exploration of Synergistic Effects in Cooperative Bis-Pd(II)-Catalysis

近年来，彼得斯研究小组将茂金属平面手性双环化合物FBIP和RuBIP描述为不同反应类型的立体选择性催化剂。对于这些反应中的几个，我们能够通过机理研究表明，催化剂允许双金属协同活化模式，在这种模式下，亲水性和亲核性同时被激活。对于1，4-加成反应，发现双金属活化能极大地加速C-C键的形成，即使在温和的条件下形成四元立体中心，C-C键的形成也几乎瞬间发生。另一方面，动力学和光谱研究表明，这种双金属催化目前不能最大限度地受益于合作效应产生的这种显著的反应活性，因为双金属桥联配位对产物的抑制显然比相应的单金属配合物起到更重要的作用。这一趋势大大降低了双金属催化的反应性优势，因此竞争的单金属反应路径仍然很重要，往往会导致选择性的显著损失。本研究的主要目标是开发新的平面-手性双金属催化剂，这种催化剂可以在相当大的程度上从协同效应中获益，从而产生比目前已知的双金属环更高的反应活性。这将允许更短的反应时间，更低的催化剂负载量和新的应用范围。拟议的发展可能导致催化剂，这可能接近技术规模的适用性，并允许对复杂的手性构建块采取步骤经济的方法。为了实现这一目标，我们将研究两种不同的概念，在这两种概念中，应该通过利用半裂供体来大力加速产物去复配。例如，所得到的高催化活性将用于低聚肽的步骤经济访问，其中组装了官能化的季胺基氨基酸。

In recent years, the Peters research group has described the metallocene-based planar-chiral bis-palladacycles FBIP and RuBIP as stereoselective catalysts for different reaction types. For several of these reactions we were able to show by mechanistic studies that the catalysts allow for a cooperative bimetallic activation mode, in which electrophile and nucleophile are simultaneously activated. For 1,4-additions it was found that C-C-bond formations are extraordinarily accelerated by the bimetallic activation and take place almost instantaneously even for the formation of quaternary stereocenters under mild conditions. On the other hand, kinetic and spectroscopic studies have revealed that this bimetallic catalysis can currently not benefit to a maximum level from this remarkable reactivity generated by the cooperative effects, because product inhibition by a bimetallic bridging coordination obviously plays a more important role than for the corresponding monometallic complexes. This tendency substantially reduces the reactivity advantage of bimetallic catalysis and competing monometallic reaction pathways are thus still important, often leading to a significant loss of selectivity. The major goal of the proposed studies is to develop new planar-chiral bimetallic catalysts, which can profit to a considerably larger degree from cooperative effects, resulting in a significantly higher reactivity than with the currently known bismetallacycles. This would allow for shorter reaction times, lower catalyst loadings and a new spectrum of applications. The proposed development could result in catalysts, which might approximate applicability on technical scale and allow for step-economic approaches towards complex chiral building blocks. In order to realize this goal, we will investigate two different concepts, in which product decomplexation should be strongly accelerated by making use of hemilabile donors. The resulting high catalytic activity shall, e.g., be utilized for a step-economic access of oligopeptides, in which functionalized quaternary amino acids are assembled.