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

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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.