The impact of supramolecular self-association of organocatalysts on catalytic performance.

Organocatalysis has emerged as a powerful tool in homogeneous catalysis, and especially in enantioselective catalysis. Importantly, the functional groups that are key to the reactivity of organocatalysts also allow for noncovalent interactions between catalyst molecules, both in the absence and in the presence of the reaction substrates. Such noncovalent interactions can lead to catalyst self-association, which can affect the catalytic behaviour of the respective organocatalyst, in terms of both reaction rates and enantioselectivities. In this Review, we present examples of such catalyst self-association in various organocatalysts, including ureas, thioureas, squaramides, peptides, silanediols and phosphoric acids. We analyse the known solid-state and solution-phase structures and discuss the influence of self-association in catalysis. We hope to illustrate the importance of catalyst self-association, which should be taken into account by practitioners of organocatalysis and catalyst designers.