RESUMO
Self-assembly processes of three octahedron-shaped [Pd6L12]12+ cages were investigated by an NMR-based quantitative approach. As to the on-pathway of the Pd6L12 cage assembly, the final intramolecular ligand exchange in an incomplete cage, [Pd6L12Py*]12+ (Py*: 3-chloropyridine, which was used as a leaving ligand), is the rate-determining step in the self-assembly of all the three [Pd6L12]12+ cages. Contrary to the previous finding that the self-assembly of [PdmL2m]2m+ structures (m = 2, 3) and [Pd6L8]12+ capsules from rigid multitopic ligands efficiently takes place without the formation of kinetically trapped species under mild conditions, in the self-assembly of the [Pd6L12]12+ cages, even relatively rigid ditopic ligands co-produced 100 nm-sized kinetic traps through off-pathways, which would be because the energy landscape becomes more complicated by increasing the number of components in the final assembly. It was found that when Py* was used as a leaving ligand in CD3CN, the [Pd6L12]12+ cages were produced in high yield, preventing the formation of the kinetically trapped species, which indicates that the use of Py* as a leaving ligand in CD3CN is effective to obtain the thermodynamically most stable species.
RESUMO
The self-assembly processes of two kinds of octahedron-shaped M6L4 cages consisting of cis-protected Pd(II) complexes and organic tritopic ligands were investigated. Whether kinetically trapped species larger than the cages are produced or the M6L4 cage is assembled without the formation of such kinetic traps is determined by a balance between the rates of oligomerization and intramolecular cyclization, which is affected by slight changes in the chemical structure of the tritopic ligand. A numerical analysis of the experimental data based on a reaction network model where 249 reactions between the possible 56 species were considered revealed the self-assembly pathways of one of the two M6L4 cages.
