Pyrene-Functionalized Ru-Catenated Metallacycles: Conversion of Catenated System to Monorectangle through Aging

Molecular transformation behavior within a mechanically interlocked system is often assisted by chemical manipulation, such as the inclusion of guest molecules, variation in the solution concentration, or swapping of solvents. We present in this report the synthesis of ruthenium metal and π-conjugated pyrene-based (2 + 2)₂ catenated rectangles. Additionally, we discuss the structural conversion of these catenated rectangles into monorectangles through adjustments in concentration and solvent composition. In the presence of a methanol solution, a transformation into monorectangles was observed as the concentration declined. However, interestingly, in the presence of a nitromethane solution, an alteration in conformation to monorectangles was noted by just standing at room temperature for a few hours without any chemical manipulation. Furthermore, theoretical calculations were studied to provide insights into the formation of catenated structures over other potential ring-in-ring or Borromean-ring-type structures. The computational study with the GFN2-xTB method combined with density functional theory (DFT) calculations showed that the lower binding energy within the rectangles favors a catenated structure over other potential ring-in-ring or Borromean-ring-type structures. This work represents a new example of an intertwined structure that self-assembles into a catenated ring rather than a ring-in-ring or Borromean ring and transforms into a monorectangle in nitromethane without the use of any template, alteration in solution concentration, or exchange of solvents, but simply by standing at room temperature.