Solvent-Dependent Self-Assembly Behaviour and Speciation Control of Pd6L8 Metallo-supramolecular Cages

The C-3-symmetric chiral propylated host-type ligands (+/-)-tris(isonicotinoyl)-tris(propyl)-cyclotricatechylene (L1) and (+/-)-tris(4-pyridyl-4-benzoxy)-tris(propyl)-cyclotricatechylene (L2) self-assemble with Pd-II into [Pd6L8](12+) metallo-cages that resemble a stella octangula. The self-assembly of the [Pd-6(L1)(8)](12+) cage is solvent-dependent; broad NMR resonances and a disordered crystal structure indicate no chiral self-sorting of the ligand enantiomers in DMSO solution, but sharp NMR resonances occur in MeCN or MeNO2. The [Pd-6(L1)(8)](12+) cage is observed to be less favourable in the presence of additional ligand, than is its counterpart, where L=(+/-)-tris(isonicotinoyl)cyclotriguaiacylene (L1a). The stoichiometry of reactant mixtures and chemical triggers can be used to control formation of mixtures of homoleptic or heteroleptic [Pd6L8](12+) metallo-cages where L=L1 and L1a.