Exploring the Synthesis of Metalloporphyrin Equipped Pd ₁₂ L ₂₄ Supramolecular Spheres

ABSTRACT

The range of metalation states within porphyrins provide a facile approach to tunable optical, electrochemical and catalytic properties. Spatial organization of metalloporphyrin units can yield additional emergent properties, with precise organization in Pd ₁₂ L ₂₄ (L = Ligand) supramolecular nanosphere systems made possible by metal‐mediated self‐assembly. Here, we explore synthetic approaches to form porphyrin‐appended Pd ₁₂ L ₂₄ nanospheres, featuring porphyrins with different metal centers. New synthetic strategies are devised and explored en route to porphyrin‐equipped nanosphere building blocks. We determine that Pd ²⁺ , Cu ²⁺ , Fe ³⁺ , and Zn ²⁺ metalated porphyrins can withstand the nanosphere formation process, while Mg ²⁺ porphyrins experience transmetalation under nanosphere formation conditions. The free base porphyrins are easily metalated by the metal precursor [Pd(MeCN) ₄ ](BF ₄ ) ₂ , required for Pd ₁₂ L ₂₄ nanosphere formation, but free base porphyrin‐containing nanospheres are readily formed under kinetic control when the precise stoichiometry is employed. With these newly developed synthetic methods, porphyrin‐equipped building block compounds can form Pd ₁₂ L ₂₄ nanosphere assemblies with porphyrins placed at both the exohedral and endohedral sites of the supramolecular construct. The cage‐appended porphyrins retain metallation state dependent optical properties, although transient absorption measurements reveal much faster photophysics than molecular controls. Therefore, porphyrin‐containing supramolecular nanospheres can now be explored as energy transduction systems with potential applications in artificial photosynthesis.