Coordination Chemistry of a Star of David [2]Catenand

Mechanical interlocking can profoundly alter coordination environments, yet its influence on metal-ligand self-assembly remains underexplored. Here we report on the coordination chemistry of a Star of David [2]catenane comprising two triply interlocked macrocycles, each containing 9 bipyridine units, and show that preorganization within this topologically constrained ligand fundamentally reshapes metalation pathways. Direct metalation with Fe(II), Co(II), Ni(II), or Cu(II) leads to kinetically trapped, ill-defined products, whereas Zn(II) rapidly and reversibly reforms a well-ordered hexanuclear catenate. Exploiting the lability of Zn(II)-bipyridine coordination, we demonstrate a stepwise transmetalation strategy that enables clean, quantitative access to the Fe(II), and otherwise inaccessible Co(II), Ni(II), and Cu(II), Star of David [2]catenates. Time-resolved mass spectrometry reveals discrete heterometallic intermediates, supporting a mechanism that minimizes large-scale mis-coordination and ligand reorganization during stepwise metal exchange. Single-crystal X-ray structures of the Co(II) and Cu(II) analogues confirm retention of the Star of David topology and reveal persistent incarceration of a counterion within the central cavity, even following other anion exchange and/or transmetalation. Partial crystallographic data for the Ni(II) system and spectroscopic consistency of the Fe(II) and Zn(II) analogues support structural conservation across the series. Oxidation of the Co(II)₆-Star of David catenate smoothly affords the Co(III)₆-analogue. Isothermal titration calorimetry shows that the Star of David catenates bind iodide within the central cavity with metal-dependent affinities reflecting both the coordination geometry and the residual anion occupancy. Together, these results establish stepwise transmetalation as a strategy for overcoming kinetic barriers in topologically complex coordination assemblies and highlight mechanical bonding as a design element for controlling metal ion reactivity and guest recognition.