Conjugation Effects in the Generation of Dynamic Covalent Libraries of Bis-Imines from Substituted Aromatic Aldehyde and Amine Components

The conjugation-driven stability and reactivity of bis-imine formation from the reaction of substituted aromatic aldehydes and amines bearing electron donor and acceptor groups were studied in two approaches involving aldehydes and amines with the substituents either conjugated (para position) or non-conjugated (meta position) to the reacting functional groups. The bis-imine from the reaction of a bis-amine (B) with different types of aldehydes (A) constituted an ABA module, whereas the reaction of bis-aldehydes with different amines resulted in a BAB module. The competitive reactions were also studied for a specified bis-amine (B1 or B2) in similar conditions with a mixture of different aldehydes, and the time-dependent generations of dynamic covalent libraries were followed. The results indicated that conjugation modulated the bis-imine formation. The reaction of the conjugated bis-amine B1 with a mixture of two different aldehydes A1 and A2 favoured the formation of the bis-imine A1B1A2 involving different aldehydes. The results of the study provide insights into the effect of conjugation on the reactivity and stability of bis-imines and provide a basis for inducing selectivity features in the formation of bis-imines from different types of aldehyde and amine groups. They provide an entry into the design of dynamic covalent libraries generated from extended multicomponent systems.