Selective Synthesis of Molecular Borromean Rings: Engineering of Supramolecular Topology via Coordination-Driven Self-Assembly

Molecular Borromean rings (BRs) is one of the rare topology among interlocked molecules. Template-free synthesis of BRs via coordination-driven self-assembly of tetracene-based Ru(II) acceptor and ditopic pyridyl donors is reported. NMR and single-crystal XRD analysis observed sequential transformation of a fully characterized monomeric rectangle to molecular BRs and vice versa. Crystal structure of BRs revealed that the particular topology was enforced by the appropriate geometry of the metallacycle and multiple parallel-displaced pi-pi interactions between the donor and tetracene moiety of the acceptor. Computational studies based on density functional theory also supported the formation of BRs through dispersive intermolecular interactions in solution.