Solvent-dependent self-assembly behaviour and speciation control of Pd 6L8 metallo-supramolecular cages

The C3-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 PdII into [Pd6L8] 12+ metallo-cages that resemble a stella octangula. The self-assembly of the [Pd6(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. All sorted: Stella octangular [Pd6L8]12+ metallo-cages with chiral propylated cyclotriveratrylene-type ligands exhibit homochiral self-sorting in MeCN or MeNO2 but not in DMSO. Furthermore, differences in the favourability of the metallo-cage with propylated or methylated ligands can be used to control speciation in solution from heteroleptic to predominantly single homoleptic to dual homoleptic metallo-cages.