Interplay of Interactions Governing the Dynamic Conversions of Acyclic and Macrocyclic Helicates

Systemic change : A system of transformations between helical structures was observed to be governed by interactions mediated by the electronic effects of substituents, entropic effects, the conformational preferences of organic building blocks, and the coordinative preferences of the metal ion. All of these effects were important, but all must be considered together to allow the prediction of the product observed (see scheme). magnified image A rigid, helical macrocycle that contains two copper(I) ions has been synthesized through subcomponent self‐assembly. Although it does not obey the “rule of coordinative saturation”, this macrocycle could be prepared through subcomponent substitution starting from a tri(copper(I)) helicate, in a reaction in which copper(I) was ejected. The macrocycle was observed to readily participate in a sequence of transformations between helical structures mediated by the electronic effects of substituents, entropic effects, the conformational preferences of organic building blocks, and the coordinative preferences of the metal ion. The thermodynamic parameters governing the interconversion of an “open” helicate and the “closed” macrocycle were determined through van ‘t Hoff analysis, allowing quantification of the entropic driving force for macrocyclization.