A Multi-Stimuli Transformational Network of Benzil-Based Pd(II) Assemblies

Achieving precise control over supramolecular topology and nuclearity in coordination-driven self-assemblies through integration of multiple stimuli remains a challenge. We here introduce ligand L^A, based on a flexible and reactive 1,2-dicarbonyl benzil-based backbone, able to adopt several conformations. A range of homo- and heteroleptic Pd(II) assemblies is formed with different nuclearities and topologies, connected through distinct transformation pathways. In homoleptic systems, folded and open conformations of L^A afford the mononuclear complex PdL^A ₂ and the lantern-shaped cage Pd₂L^A ₄. Incorporation of secondary ligands L^C or L^D induces more expanded L^A conformations, yielding cis-Pd₂L^A ₂L^C ₂ or a rare isosceles triangular Pd₃L^A ₂L^D ₄ ring. These heteroleptic architectures can be interconverted, and both can undergo guest-induced retro-cage-to-cage transformation to regenerate homoleptic species. Furthermore, L^A can also be conformationally locked through condensation of its benzil backbone with 1,2-phenylenediamine, producing the rigid quinoxaline ligand L^B. This transformation can occur in a post-assembly fashion, converting both homoleptic and heteroleptic L^A-based structures into the PdL^B ₂ complex. The conformation and accessibility of L^A reactive sites within the architectures, as well as the nature of the encapsulated guest, strongly influence assembly stability and reactivity in this condensation, reminiscent of how nature controls functional group reactivity through effects of nanoscopic confinement, conformational restriction, and allosteric regulation.