Precise modular engineering of neutral organometallic rectangles from binuclear palladacycles via hierarchical assembly strategy

Abstract Metallosupramolecular assembly provides a powerful strategy for the precise construction of well-defined architectures with diverse topologies and functionalities. However, the construction of neutral organometallic architectures supported by robust metal-carbon bonds remains underdeveloped, largely because kinetic persistence limits the reversible structural correction required for conventional self-assembly. Herein, we employ binuclear palladacycles as intrinsically neutral and geometrically preorganized building blocks and develop a hierarchical assembly strategy that temporally separates geometric programming, scaffold editing, and topology locking. Through a polymerization-cleavage-assembly process, cyclopalladated polymers are converted into discrete binuclear precursors while retaining their programmed geometrical information. Subsequent trans-effect-directed N -heterocyclic carbene ligation affords a series of size-tunable, kinetically robust, and neutral organometallic rectangles. The resulting architectures are fully characterized by spectroscopic methods and single crystal X-ray diffraction analyses. Moreover, single crystal X-ray diffraction identifies guest-mediated breathing-like geometric deformations in the solid state, driven by exo-wall π-π stacking and charge-transfer interactions with both electron-rich and electron-deficient planar guests. This work establishes a hierarchical construction principle for accessing discrete neutral organometallic architectures by separating geometric programming from the final locking of the topology through strong bond formation, while demonstrating that local geometric adaptation can occur without disrupting the framework connectivity established by Pd-C bonds.